I also read the IGN article on how karlachs quest was ''never cut'', pretty infuriating to read not gonna lie. Larian doesnt seem to think karlachs questline is unfinished, maybe for PR reasons. That or they genuinely find her linear storyline with a unavoidable tragic ending to be good, despite all the other origin characters getting much more fulfilling questlines and satisfying conclusions. Sure, the avernus ending cutscene and the new epilogue give more hope to the avernus ending, and a hint that shes gonna get fixed and escape hell, but boy would i have loved to PLAY that story in the actual game larian!
Hell, larian stated that they were surprised people wanted a longer epilogue and humbly admitted they made a mistake in not creating that for the game, promising to add a proper epilogue later (which they now have). The fact that they dont seem to show a similar sentiment to karlachs story makes me fear theyre never gonna do any changes to her quest and just leave her avernus quest open ended. It sucks ass
It also doesnt help that karlach has much less dialogue in the epilogue than most other companions, especially if you accompanied her to avernus, so if this really is the last update to karlachs story that just makes this entire situation even worse.