Its must be a trend in gaming industry of not giving player happy ending Far Cry being doing this since Far Cry 4, no matter what you do you always get shitty endings difference is that you want (A) Shitty ending (B) Extra shitty ending (C) Totally shitty ending.
Same here only option with Karlach here is let her die, she become mind flayer, or trapped in hell while she being hunted, and even more shitty is that she found solution for her heart but only if you play as origin Karlach no solution for companion Karlack because if they do they have to add more for Karlach as romance option after her cure and in her quest line which they did not that why if you chose to go with Karlach to hell with her, game just end right there no slideshow no nothing after story it just end. You invest so much time to be just shit all over at the end.