I think it's also a big problem with writing something set in Faerun. Lots of things are technically pretty easy to solve, but the writers have to pretend it isn't to tell the story they want to tell, set in a universe that has a LOT of things and solutions for conditions written over the decades.
Just typing that out made me realise that, for example, if SH decides to save her parents, I don't see why she couldn't chop her hand and have something like Regenerate cast on her later or get a prosthetic hand or something, because there's a precedent for that here. But the story they wanted to tell wouldn't work ""realistically"" (by this I mean within the established rules of the universe) if that were something she set out to do.
That is not to diminish the frustration felt- I like Karlach, but she's not my favorite character and I don't romance her, so I can't completely put myself in the posters in this thread's shoes. This is my point of view from someone who enjoyed her casually, but I do get how if you love her, seeing her story get cut short while others get to live on pretty happily feels like a kick to the gut.
