Drawing a parallel to another character (who, no, did not draw the short stick as badly as Karlach - not even close): Astarion
He gets his sweet but slightly bitter ending in the option to keep him on the “good” side of grey. If you do that, he will have to give up being in the sun because he will remain a spawn. But in his epilogue, there is mention that, from then on, tav and him will journey on to find a way to help him be in the sun again. It’s not a certainty, but it’s a hope that it could be possible. This little nugget of hope can help carry his story’s conclusion even more to the happy side of things.
Tbh, the “go back to Avernus” ending could’ve implied something in similar lines. Yes, perhaps there’s a fix - but not where we hoped. Maybe the chance to fix her is what will take the player and herself back to the Hells.
Karlach’s story is flawed beyond this, yes, and I’ve written about it here before. However, a small change like this - implying there’s hope for her, but at the cost of more challenges - would make the entire story as it is much easier to swallow.
