I want to believe that such incredible plot holes in Karlach's story are due to the fact that she was remade from scratch so many times and simply did not have time to give her a quest line worthy of the original character. I really don’t want to believe that Larian will stubbornly insist that Karlach is doomed and the only way for her to survive is to return to Avernus with her, only to make her a “tragic character.” Even if they really want this, it does not fix the problem that the player essentially has NO influence on her fate and this is truly unforgivable for any game that calls itself an RPG, where at all times the player's choice has been one of the most important parts. At the moment we have no choice regarding Karlach other than "neutral", "bad" and "very bad".
I am once again asking you to let us fix Karlachs engine so her ending isn't decided by a dialog box in the last 30 seconds of the game!