I’m not a big FR lore nerd, but isn’t the Mystra of the “present” day a different person than Mystryl/Mystra, who took over the portfolio much, much later than Karsus’s Folly? If so, then it’s not clear why Karsus would feel the need to apologise to her or why she’d feel the need to punish him now. I mean, I suppose it might be the principle of the thing but it wouldn’t be personal.

I’ll be honest, while I enjoy stories that tie in with the wider lore, and disagree with the folk who think it’s already too much that Gale’s backstory is that he used to be arch-wizard level powerful, I hope we won’t see anything quite as epic as Gale being Karsus reborn. At the moment, what I’m hoping for/guessing is that he was one of the new Mystra’s Chosen recruited after her resurrection, perhaps a decade or so before the events of BG3.

EDIT: Though that’s just my preference for the BG3 game! If Gale=Karsus is a theory you think you think you can get some mileage from and is an idea you and your TT group are excited about, then why not?! I didn’t mean to rain on anyone’s parade smile.

"You may call it 'nonsense' if you like, but I've heard nonsense, compared with which that would be as sensible as a dictionary!"