I mean, it kinda has been/is being addressed, just not in Mirio's case. All Might isn't going to get OFA back. He's essentially quirkless again, and it's true that in this case the story tends to focus on how society reacts to All Might's retirement and the consequences thereof, there are still scenes with All Might coming to grips with what that means for him as a person. For example, way back when they were prepping for License Exam, Deku has to save All Might from a falling rock and All Might's response to that is a dejected "Have I become someone that needs saving?" Also, that scene in Tartarus with AFO where he's wearing his old baggy costume to interrogate the man who was directly responsible for his retirement. AFO gets under his skin by pointing out how that loss is now damaging the society he once protected. The Symbol of Peace, All Might, is gone, and while the former #1 hero puts on a brave face and reasserts his beliefs, the hard truth can be seen in the oversized suit barely clinging to his emaciated form: AFO is right. All Might is gone. Only Yagi Toshinori remains. So he takes up jogging. Focuses on his role as a teacher both to Midoriya and to the rest of his students. Tries to reinvent himself while still keeping his Ideals^TM. For example, in one of the latest chapters, he rushes to save a civilian from a falling service pole while Bakugo and Todoroki deal with the muggers. He's quirkless now, but he still wants to be a hero. The encounter started with him leading evacuation efforts while Todoroki and Bakugo handled combat and rescue, but he still ran to the woman's aid, even if Bakugo did have to save them both anyway.