I love the idea of the ending - he reached his goal, though short-lived, but still vanquished the worst evil in the world in that little amount of time. However, I still see another possible ending. If Eri can rewind a person, including their Quirks, couldn't she have rewound One For All? If she can rewind Quirs to the point that they don't exist anymore, couldn't she rewind Quirks to the point where they exist again? In Heroes Rising, One For All transferred itself back to Deku without Bakugo intending to. So even if it WAS transferred to Shigaraki, couldn't it be returned to Deku? And if it being returned to him weakened it, then couldn't Eri reinvigorate it?