If anyone is thinking I make too many death comments, here's why:
This will be divided into two sections: 1.) Comments about characters who are dead, or else about whether they are dead. 2.) Speculation of deaths to come in the future.
Not a revival of the Chrysalis/Sombra status debate
In the case of characters that are either dead or could be presumed dead, the reason I don't like people speculating that they survived is because I don't want to think the show doesn't have the... I don't know if I can say the b word here so I'll say guts... to kill even a villain. Because kid-friendly shows do it all the time. Disney movies, non-Disney movies such as The Swan Princess, Quest for Camelot, or Anastasia, Pokemon (and half of its deaths weren't even villains), even G1 of My Little Pony (Tirek and Lavan). Any kid who's seen just about any Disney movie aside from the two furry ones (Robin Hood and Zootopia) will have seen death in a movie.
I might give particular mention to the original dub of Sailor Moon, which removed the inappropriate content from the first two seasons and I think the fourth (haven't seen in a while so I can't remember), and for this, people called it childish and accused it of being only for little girls as well (I even thought so once before a dream led me to do some research and discover the truth, which is why I'm so sensitive to comments like that), despite the fact that almost all of the deaths remained uncensored, even Neflite/Nephrite (who is impaled by thorns in bloody fashion after he had reformed), and almost every episode killed a character. If people would think that about a show with twice the body count of James Bond, what would they think of a kid-friendly show based on a line of toys aimed at little girls that is afraid to destroy a pure evil villain even in a family-friendly way? What do a lot of people think about the show and the fandom already (although I heard that could be dying down)?
Even Yu-Gi-Oh, which was often ridiculous when it came to censoring deaths (especially since they often replaced it with eternal damnation to its hell, the Shadow Realm), up front killed the Big Five, Gozaburo, Dartz, Bakura, and Zorc (Yami Marik and the Great Leviathan maybe but they did say "Shadow Realm" and "banish", respectively), even though the Big Five's deaths were postponed eight episodes when instead of deleting them, Noah imprisoned them in the virtual world which would eventually be destroyed with them in it, by which point they had likely been forgotten.
Granted a lot of the shows I mentioned above, including Sailor Moon, have killed non-villainous characters too, which is a place MLP certainly doesn't go in G1 or G4. While they could probably get away with it at this point, they don't want to get too heavy and make it as lighthearted as possible, even with the presence of dark villains to appease those of us who like the more epic moments, and if it can have villains like that, it shouldn't be afraid to dispose of them that way. FiM is actually lighter than G1.
I know it might seem a bit morbid for me to think along the lines of "it's no fun if no one dies", but no more so than people who like their shows to be grimdark and prefer to see heroic characters die over villains. Another note, if the show didn't have villains like that it might be a different matter. I did do some research on the Barbie movies, which didn't sound like they had the appeal of MLP, and a lot of them did have villains - all of which lived.
Here I shall list all the potential deaths here and rating them 1-4, with 4 being definite death unless you have a big headcanon that they survived, 3 being can easily be presumed dead, 2 being can vaguely be presumed dead, and 1 being the possibility of death is a huge matter of headcanon. Also comics will not be taken into account here, only the show.
- Starswirl the Bearded and the founders of Equestria - 4. Obviously they'll be dead of old age since they lived a thousand years ago and only alicorns and centaurs seem to be immortal.
- Windigos - 3. They are last seen incinerated by the Fire of Friendship, never seen again. A Windigo howl is heard in the present, but as they'd never threatened to return during any other arguments before, this could be somepony imitating one to break up the fight.
- Fuzzy Slippers - 2. He is shown in the hospital with a shaved head, implying cancer, and in the next episode, a funeral is shown, though it is not specified who.
- Queen Chrysalis and her changelings - 3. They are blasted over the edge of Canterlot by Shining Armor and Princess Cadance. I say Chrysalis fell to her death, but due to the fall being staged like Team Rocket who always survive, many are sure she survived, that she's immune to long falls or else faster than Rainbow Dash (some saying the former based on the comics alone). Their fate is unconfirmed and so far we're free to make up our own minds. At least one changeling, Kevin, is seen in the present, but he could have either landed in water or not taken part in the invasion ever, friend of Matilda.
- King Sombra - 4. He is shattered to pieces by the Crystal Heart and nothing in the show has hinted at his survival. Even if you take the comics into account he was a ghost and Hope resurrected him.
- Princess Amore - 3. Comics aside, it is never specified what happened to her when Sombra took over the Crystal Empire, but given her absence in the present day Crystal Empire two things are highly likely: Either Sombra killed Amore when he took over, or she was outside of the Crystal Empire when it disappeared, and is likely dead of old age (even if she was an alicorn, only Celestia and Luna are immortal).
- Pinkie Pie clones - 3. They are zapped by Twilight with magic, collapsing them into magic which is sent back into the Mirror Pool. The fact that they go back in instead of disappearing outright implies they are imprisoned there; since they came from nonexistence, however, it is likely they returned to nonexistence. One can also question whether they were truly "alive" even when they did exist.
- Pinkie Pie - 0. I've heard very light speculation that Twilight actually killed her and left one of her clones by mistake, but they made it very clear that it was the real Pinkie there instead of pulling the classic trick usually seen in this scenario, and given her character development and background with her family and such (where the clones couldn't remember Applejohn's name), this is further confirmed in later episodes.
- Applejack's parents - 4. Though we never really did get to know them and thus they weren't strictly killed in the course of the show, this has been speculated and debated for some time, but was essentially confirmed by the two shooting stars in Apple Family Reunion, and Applejack's "if Mom and Dad were here" comment in Crusaders of the Lost Mark.
- King Timberwolf - 3. He chokes on a rock thrown into his mouth by Spike. The reason this is debatable is because he shatters to pieces afterwards, and Timberwolves are known to come back together after shattering to pieces, like Dry Bones.
- Plunderseeds - 4. They are destroyed outright when Twilight returns the Elements of Harmony to the Tree of Harmony, but they are often overlooked because they're just vines.
- Chimera - 2. Her tiger's head and snake's head were trapped in a tree trunk and tree branches by Applejack, and so she can be presumed to starve to death, though her fate will be prolonged since Applejack gave the goat's head some cheese even though she was no longer a threat at this point.
- Rarity Cloud - 2. Destroyed by Luna with moonlight, but one can question whether she was even alive in the first place since she only appeared in Sweetie Belle's dream.
- Lord Tirek - 1. He is de-powered and imprisoned in Tartarus by the Mane 6 with Rainbow Power. If one wants, they can say they did kill him on account of Tartarus being hell and presume that villains spend their afterlife imprisoned in cages in Tartarus, like Frieza spends his afterlife imprisoned in a cocoon in hell. But anyone else, the simpler answer is they took away his power and reimprisoned him there through teleportation and conjuring a cage out of thin air.
- The Dazzlings - 2. They were kept alive as humans by the power of their pendants for over a thousand years, and when the Rainbooms destroyed those pendants, they lost all power and their immortality. Though we see no signs of it for a few moments before they run off stage, it is likely that No Immortal Inertia kicked in causing them to age to dust, although DHX could always make an exception to that rule and have them return for redemption if they so wished.
- Arimaspi - 4. He fell into the Abysmal Abyss and we see his skull at the bottom. This is the most definite death of the show.
- Bugbear - 2. They said the Mane 6 defeated him, though it is never specified how. This gives us numerous ways to speculate on how they could have defeated the Bugbear. Did they kill him in a way too violently to be shown? Did they give him the Tirek treatment with Rainbow Power? Did Rainbow Dash Rain Nuke him? Or did they simply force him through the portal of Tartarus leaving Cerberus to guard him? Who knows - it's a mystery.
- Tantabus - 3. We're not entirely sure the nature of the Tantabus's defeat. Like the Pinkie Pie clones, it came from nonexistence, created by Luna to punish herself for what she did as Nightmare Moon. Once Luna is able to forgive herself, the Tantabus is absorbed by Luna and disappears. We're not sure whether it's dead or whether it's simply part of her now like the Gebbeth in Earthsea (who incidentally is portrayed by Mark Acheson the voice of Tirek).
- Plant Monsters - 4. Whether or not the main monster survived being tackled by Rainbow Dash, all of them were disintegrated up front by Sci-Twi's device.
- Snowstorm - 0. It is destroyed up front, but like the meteor from Armageddon, it was never truly alive to begin with so it doesn't count.
- Dr. Caballeron, Rogue, and Withers - 2. They were last seen being chased by the temple dragon (forget the name). If they don't reappear, I'll say they were eaten, but their return is still possible.
Nightmare Moon is not listed because in the show it is specified that she and Luna are one and the same. In the comics of course it is a different matter, and she is destroyed by Spike through his love for Rarity.
Speculation of deaths such as Rarity or Luna
This was in the past when I thought that this show would kill them off, Luna in the Season 4 premier when we thought she was turning back into Nightmare Moon and thus could not be truly redeemed, and Rarity during or after Season 3 in which she had no episodes to her own and was treated quite badly in the comics. Further supported by the fact that Hasbro let DHX see her punched in the face (and I wonder whether they'd have approved a certain scene in the comics for anypony besides Rarity) when they wouldn't let it happen to Tirek, as well as the fact that a lot of my favorite characters seem to die in shows, except Daryl Dixon and Tyrion Lannister who are in the Top 10 most mature shows I've seen.
But this is all in the past, because they've now made it very clear that they aren't going to kill a non-villainous character, especially a main character. Exception being the extremely minor and subtle Fuzzy Slippers, or anypony who's dead by the story's beginning. There is light speculation that they'll "kill" Celestia and Luna in an equally subtle way by having them simply "ascend", "fly", or "ride" into Heaven in a similar style to Frodo, Bilbo, Gandalf, Elrond, and Galadriel in Lord of the Rings, but even this is a longshot and I am confident all the Mane 6, Spike, the CMC, Starlight, and the princesses will still be alive by the end of the 2017 movie.
After a certain point, any comments on the matter were to reassure others that none of them are going to die in upcoming episodes.
On a side note, any fear that Rarity is going to leave the series in any way is unfounded because they are clearly trying to make up for Season 3 by giving Rarity more and more episodes, to the point that people here are starting to say that she's the main character now. DHX won't get rid of one of the Mane 6 even in a deathless way, besides, she's even funnier than Pinkie Pie and can be almost as adorable as Fluttershy so we need her.
So, I am not expecting them to kill even Starlight, Discord, or Trixie. It is true that Starlight won't take part in the Mane 6's adventure, but she'll probably be either staying somewhere else in the movie, or else imprisoned by Cosmos. I could expect Cosmos to be killed, but only because he's the villain and outright evil villains are fair game anywhere, ranging from MLP to Game of Thrones.