I do agree that Astarion’s good ending gives him closure. He talks about how your faith in him makes him feel good, and he realizes he can love himself for who he is and what he is, and still be a good person, regardless of what he used to do. He even says that “While the Sun is nice, it’s overrated and the night is much more my thing” and that being an adventurer is nice since he learned you can kill and drink the blood of whoever you want as long as they’re criminals, and no one really cares.
Gale also arguably still gets a good ending. While Gale is clearly told to be power hungry, he’s also a good person at heart and he usually listens when people talk him down off power-hungry cliff edges. For example, he ends up not giving the crown to Mystra and just becomes a professor at a college for Magic in an ending. He seemed rather happy about it because he just loves talking about magic all the time.
Karlach’s ending at this point can be called a positive one, but there’s clearly a better one to develop (whether that be more for this ending or a new one with a fix) and there’s also the fact that unless you turn into a mindflayer or she just dies, her Avernus ending doesn’t have any sort of closure for the player. Well, it does, but it’s left up to the players imagination, and I personally think that’s a dropped ball, since it’s really only her. Of course, this could always kinda just be an open-ended ending until Larian adds one that gives her an actual fix of some sort like you’ve mentioned, but I can’t confidently say myself if I believe that’s the case or not. I personally believe (I try too at least) that because she was added so late in the development, that’s why her endings are what they are (because she’s the only one in this weird situation) and that she’ll be reworked on for the Enhanced Edition like Beast was in DOS2. Of course, it’s no guarantee, but I believe the community reaction around Beast was pretty similar to Karlach’s, except Karlach’s has just been louder since BG3 is more wide-spread.
