I wonder if this with play differently without Karlach in the group. Though I'm not sure I'd be willing to abandon her for a playthrough to find out.
It doesn't. I've played without her. Astarion runs off and then it just cuts to the scene of the city celebrating lol. So before they added the epilogue if Karlach wasn't in your party that was the last companion scene. (Unless you romanced one of them.) It's like comically bad and bewildering.
So even if you don't have to help Karlach, you can't help Astarion? Ugh that's frustrating.
I keep wondering if they made some way to help him that no one's found yet, but that's probably just copium. This can't possibly be the only option for spawn, right???