I can imagine them doing a thing where Karlach’s quest doesn’t end at the Last Light Inn, but instead continues into the part with the Steel Watch factory and the Gondians (which I don’t know much about, tbh, because I haven’t played it yet), before concluding in a final, very obvious dead end.
For example, maybe when you first enter that overall area, you and/or Karlach would be pulled into a conversation with some important, plot-relevant NPC and you’d be able to ask them about fixing the infernal engine, and they’d be like “oh yeah, talk to this other person over in (other area of the city that you haven’t visited before), they’d definitely be able to fix the engine!” And then you make your way over there, but maybe in order to get to this person, you’d have to go through a really challenging, super high security dungeon area—like you’d have to get through a really hard stealth section or fight lots of really tough enemies or pass a bunch of high skill checks or some combination of all of those, and maybe there’d also be some sort of special environmental challenge/puzzle that you’d have to really think about, like how you had to use the lava and the hammer to defeat Grym. And then, when you finally get to the place you were told to go, you discover that something horrible happened and the entire place has been completely destroyed, and the only thing that’s left is a burnt shell of a building and a whole bunch of corpses, including the corpse of the person you were told to talk to, and that corpse just has like a single gold piece and a very brief note with some vague lore-related info about how the person doesn’t feel safe here or something, and you and Karlach and the whole party have to collectively process the heartbreak of having gotten their hopes up only for them to be crushed into dust like that.
Sorry for the run-on sentence, but that’s how I would have wrapped up the quest. I feel like it would be a good way to very clearly communicate to players that no, there actually aren’t any solutions other than Avernus or death by spontaneous combustion, while also keeping the sense of player agency.
I feel like that'd be a needlessly cynical way to continue and conclude her quest, and if larian updated karlachs quest to follow this similar line of storytelling in the future after everything players have been saying in regards to karlachs railroaded, tragical ending i think hell would break loose lol. Its already depressing enough to replay the game and know that her fetch quest wont amount to granting her a different ending, if we now also would have to spend more time to do a longer quest and know it wont matter jack shit then I feel like that'd ruin the game for me even further.
If they really felt adamant on not letting us cure karlach, i'd rather they spent time on having certain npcs give us more clarification on why her heart cant be cured, like maybe its some zariel/hell related magic or something (raphael could say this maybe? or some other npcs whos more reputable than fucking dammon lol). Additionally, please give more reactivity from the party members on her situation and maybe have them give their opinions to karlach on whether she should return to avernus to find a cure or die in faerun. Hell, even just let tav/durge that doesnt romance her spend time with her and give her more comfort for gods sake, in general it just feels like nobody cares about whats happening to her.
But imo thatd still feel frustrating because ultimately she'd still have the same, railroaded ending unlike the other origin characters, and i still personally cant wrap my head around WHY she has to have a tragic ending in a game setting like this where so much other wild shit that should be killing our protagonist or companions doesnt. The argument ''karlachs story is meant to be tragic'' just sounds too dogmatic for me. So i'd still prefer a questline that allows us to fight for curing her
