Anyways it's time for MY unpopular opinion, and my unpopular opinion is that if Horikoshi does decide to kill All Might off it will be a very, very poor writing decision. Which isn't a new concept to Horikoshi, so who knows. But everyone seems to think that All Might is going to die before the end of the series and I just think there's absolutely no compelling reason for that to happen.
First of all, this series has enough martyrs as it is. Like honestly, Nighteye was enough all by himself, and even his death has hardly been paid off in character development for the people he was supposed to be character development for. The only people who have changed drastically because of his death are Ochako and Toshinori, and even Toshinori's Nighteye-related character development didn't happen until almost a hundred chapters after Nighteye died. We have yet to see how Izuku or even Mirio has been strongly affected by his death. This isn't even to mention that with Midnight and Star also dead, there hasn't been a chance to mourn either one of them or see how their deaths affected the characters they should be affecting, and honestly, there wasn't ANY reason that either of those two characters had to die. It was just senseless shock factor, because the story as it stands could still function perfectly well with Midnight being alive, or with Star being alive and simply being Quirkless.
Taking all of that into account, long story short, Horikoshi isn't great at writing death in general. He kind of just kills characters, the connected characters are sad for like one chapter and then their relevance is removed from the plot.
But more than that, deciding to kill Toshinori off would undo a CHUNK of his own character development and it would make THIS scene between Aizawa and Toshinori virtually pointless:
When Nighteye and All Might broke up, it was because All Might refused to retire, and Nighteye knew that if Toshinori kept trying to be a hero he would die a gruesome death at the hands of some villain. He said that he couldn't support Toshinori if supporting him meant just watching him kill himself. But for Toshinori, it was completely different. Nighteye's decision to look into his future was a death sentence. From his knowledge, the futures that Nighteye predicts are unchangeable. They are plain fact. No matter how many different ways you try to prevent the outcomes he predicts the best that can happen is slowing them down, but his predictions would always catch up eventually. Knowing this, Toshinori decided it was better to run headfirst towards his own death instead of simply waiting around for it to happen. If he retired, he would still be killed, and he would have sat idly by while there were people who needed to be saved. But if he was going to die no matter what, he might as well go out still carrying the world on his back.
So for him, after Nighteye's death, to have realized at the same time as Nighteye that the future can be changed, and to then decide "I'm going to live" because of it is arguably the most important piece of character development that Horikoshi has given to Toshinori. Toshinori isn't suicidal anymore. He doesn't feel like death is the only outcome. He's learning how to live with the fact that he can't be a hero anymore and is learning what he can do for the people he cares about, and for the world. He's decided to slow down. Stop running. Live for the people who love him and for the people he loves.
All this to say, of course he's going to die eventually. Everyone does. But Toshinori has decided to live, so when he dies, it should be the last time that Nighteye's predictions were proven wrong. It should be of old age, peacefully in his sleep. Not at the hands of some villain as another martyr in this story or a final battle climax.
Any writer knows that character death is usually a copout and a cheap tactic to further the growth of other characters. Keeping characters alive is much more interesting, at times much more painful, but almost always is a much more satisfying ending. Toshinori deserves a satisfying ending.
