Instead of Iron Might Making His Appearance During Final War, All Might Is The Guy In The Chair For Class A and Class B Students Who All Team Up To Take On Rewind For One.

Basically all the kids combine forces to stop AFO from getting to Shigaraki with the assistance of AM who knows how AFO fights. It's a desperate last stand that slowly and slowly begins to turn in the classes favor as they keep managing to deal more and more damage causing AFO to rewind further which causes his quirks to start bugging out.

Everyone would also take some heavy hits from AFO, deaths and major injuries would happen. However, the classes keep on pushing and trucking through until AFO eventually realizes he's taking too much damage and tries running away, allowing the kids to get a surprise attack that sends him into baby for one.