They've said before that Descent into Avernus was a 'prequel' to BG3 but there was also something called Murder in Baldur's Gate which I know almost nothing about, that supposedly deals with "Gorion's Ward" and his death. Descent into Avernus on the other hand I haven't played but know about it from Justin Alexander's blog thealexandrian, who says it has some lazy design choices and is rife with continuity errors, which is why I'm expecting Larian to change it a lot.
Murder in Baldur's Gate essentially finishes the story of BG1+2, with the final Baal spawn being killed off (no, it's not Abdel/Gorion's Ward ;)), and the God of Murder being reborn... it's an ok module, all things considered... a bit low level for the supposed gravitas of the subject matter.
Descent into Avernus I haven't played either, but judging for the EA alone, Larian is at least changing some of it...
