I feel like expecting a DLC based on the hells for Karlach is doomed to be disappointing. Because she could very likely just die. I don't think that, creatively speaking, basing a DLC on something hinging on a character who very likely dies in the game is t all a smart choice. The problem with how open-ended this game is is that trying to pick up any given thread for a DLC wouldn't work, because plenty of players may have just not picked up the thread, or may have tied it up in some way already and so picking it up again just invalidates the choices of lots and lots of players.
It doesn't 'invalidate' their choices, if they want Karlach dead in the base story, she can remain dead and won't appear in the dlc. And they won't make a dlc just for one character, Karlach being there can just be a bonus for the mission to trigger about her heart, IF you choose the Avernus ending for her. I don't get this logic of 'invalidating' player's choices in a choice based game. Besides, it just gives players more fuel to replay the game and try different outcomes. There's never one absolute (heh) choice. But if you want Karlach dead or illithid, so be it. The dlc can still reflect that.
I literally have Karlach not recruited in some of my playthroughs because I'm doing different choices and outcomes.
Not sure if I got your post 100%, do forgive me if I did miss the point.
