did you kill him? did you let him live? did you promise to let him live if he taught you to master source? did you keep your promise?
i've done all choices in various runs. in my current one, i just broke my promise to let him live, and i feel kind of bad about it. on one hand (as far as i know) he doesn't reappear in the game and letting him live doesn't negatively impact the rest of the story, but on the other hand considering what he was doing in that cave it feels like it'd be foolish to let him live
what did you decide to do?