I feel like this is something I should know but I keep overthinking it. If Magneto is the only figure in my starting force and he would be KO’ed, does the after resolutions part of his “The End of All Things” still happen?

Or does the game just immediately end when he’s KO’ed?

I think it’s the same case as a player pushes their last piece to death to kill their opponents last piece or rather when when a player kills their opponents last piece but theirs also takes mystics and dies. In is situation a the character pushing wins and in b the character attacking wins. This logic means that he does just die, and you wouldn’t take any points of pieces you happened to kill with the power.

The game does not check for a win/loss until all effects have been resolved.