The issue I think at this point is the epilogue. As of right now, it’s stated by Larian that the epilogue is suppose to give closure to the player for all of the characters stories, which it does do, unless Karlach went to Avernus. She’s still dealing with the same problem she was trying to solve the whole game. They’re put in a situation where they end up giving a post epilogue DLC where she actually gets a conclusion that the player can see (since every other origin companion gets that) or they don’t do that, and leave Karlach fans with the short-end of the stick, which would definitely upset fans moving forward.
The other solution is to give her more content in the base game, since right now it’s “Give Dammond Iron 2 times, and then Kill Gortash (who you’re gonna kill anyway)” which is rather barebones. If they expanded her base game story and actually gave us the fix in Act 3 or a hypothetical Act 4, then that means they’ll have to create a whole new epilogue for her since the current best from her going to Avernus wouldn’t fit narratively.
Larian is definitely stuck between a rock and a hard place on this one. The epilogue will definitely throw a hurdle in any plans they make for her going forward (if they decided too), on how to approach it.