I've had a theory for a while and am unsure if its been posted before but here goes.
I've always thought it was interesting how much we see Trigger in the main series and Vigilantes but no heroes have tried it. Yeah its got terrible side effects but in a desperate situation it could be the thing to make the difference.
I believe that All might will use a massive dose of Trigger to regain his powers for a few minutes in an all out brawl to the death with Tomura. Instead of only a few seconds in his muscle form, he will regain full strength and fight Tomura head on. Tomura will completely outmatch him and then kill him in front of Izuku but the fight may leave Tomura wounded. I just think it would be a fitting end to All might now, like it will not be as emotionally charged when he dies if he does so in his skeleton body.
Let me know what you think!