Since retiring and handing over the title of best hero ever in My Hero Academia, it has been more than three seasons. Since then, he has taken a backseat in the narrative, acting more as a supporting teacher to Deku and the other U.A. students. Even if it is more in the background, All Might's impact and influence on the surviving characters and the hero society are still very much present.
Since the beginning of MHA, All Might has been surrounded by death flags. This is natural; the mentor figure in a story is almost always killed off in order for the protagonist to mature. So far, All Might has survived at every turn, insisting on remaining until Deku is trained and ready to face the world on his own. With the new "Black Hero" arc of the anime, it appears that time is approaching, if not already here. So, what does this mean for the future of All Might? Would his possible death even be relevant to the plot of My Hero Academia?
All Might's Many Death Flags in My Hero Academia
As the previous generation's greatest hero, All Might has been a natural target for villains since MHA's start. His devastating stomach injury -- which continuously reduced the time he could spend as a hero -- put a dangerous time limit on every fight he was involved in. Even more worrying was All Might passing One For All on to Deku and thus taking on the role of the mentor. This figure is someone marked for an eventual death in most media, and whose passing dramatically changes the story's tone and status of its main character. It seemed inevitable that All Might would go the way of Obi-Wan from Star Wars or Dumbledore from Harry Potter in order to complete Deku's training.
After surviving his fight with All For One at Kamino Ward, it appeared as if All Might had escaped his potential death and made it to safety. Unfortunately, My Hero Academia Season 4's "Shie Hassaikai" arc introduced his largest death flag yet. In Season 4, Episode 4, All Might revealed to Deku that his estrangement with his former sidekick Sir Nighteye was because Nighteye had foreseen All Might's gruesome death at the hand of a villain within a year.
Deku was able to change one of these predictions during his fight with Overhaul -- something that had never happened before -- giving them both some relief over the certainty of All Might's death. Still, with the deadline for Nighteye's vision ever approaching, it's hard not to wonder if and when the moment of this prophecy will arrive -- and whether Deku is really able to change a future seemingly set in stone once again.
Is the "Mentor Death" trope still applicable in MHA?
Aside from My Hero Academia literally telling its audience that All Might is marked for death, the biggest sign of his demise is the previously mentioned "death of the mentor" trope that is common for coming-of-age stories. Sir Nighteye himself even fulfilled this function for both Mirio and Deku in being killed by Overhaul. However, the interesting feature of All Might's story is how he already subverted the perfect moment for his death during his fight with All For One.
By all accounts, All Might should have died at All For One's hands, which would have drastically shifted the status quo and forced Deku forward. Instead, he summoned every bit of strength he had left and found a way to win as he always had, proudly declaring that he refused to die until he could witness Izuku Midoriya come of age. While Kamino Ward was the hero All Might's functional death, Toshinori Yagi the man and mentor lived on.
All Might told Deku afterward that he fully expected Nighteye's prediction to come true during that All For One clash. However, his survival -- and making a promise to Deku's mother that he would take care of her son -- gave him the inspiration he needed to try and fight fate and live on. All Might retiring instead of dying allows him to remain a part of Deku's story and still fulfills the needs of the death of the mentor trope. Aside from a few moments such as teaching Deku how to use air force and supporting him during his vigilante arc, All Might hasn't done much as a teacher for Deku despite his promises. Still, because he's narratively fulfilled his "death" as a mentor figure, killing him off this late into the story would fail to create the emotional impact the trope typically has.
All Might's Death Would No Longer Serve MHA's Narrative
All Might has generally had little to do for the past few seasons of My Hero Academia. After passing on his mantle as number one, he acts as a source of wisdom for characters like Deku and Endeavor instead of a frontline combatant. Deku has already taken so many leaps forward since Season 3, and is in the middle of a vigilante arc that would normally follow a massive event like All Might's death. At this point, his dying at the hands of a villain wouldn't move Deku's character or power level forward; the lead has already experienced loss with All Might's retirement and Sir Nighteye's death, and is currently in a training arc where his power is rapidly increasing.
Killing off All Might now would be a cheap way to manipulate the audience's emotions or to incite a Deku rage attack on a villain like All For One or Shigaraki. All Might has been too far removed from the story for his death to have the same impact it would have had in Season 3 or 4, and, more importantly, it would have no meaningful impact on the narrative stakes. The time has passed for this death to be a meaningful narrative tool. Instead, All Might's story should continue to focus on his life after becoming the Symbol of Peace, and how he can still inspire others as a hero even without his powers.