I don't get why you keep digging in your heels about how she is supposed to be doomed because of her offering to turn into a mindflayer. I honestly don't get it. She's simply one more option that you have. You can take it, you can leave it, or you can completely miss it if you don't even bring her with you. By your logic it would also mean that Gale has to explode on the Netherbrain, since he offers. But thats a choice you get to make, isnt it?
I get even less how giving her a happy ending would somehow "retcon" all of her character. You literally do not have to change any of the stuff that we already have, you only need to add on top of it.
As for the whole "but its expensive" stuff: Sure, it costs more.Doesn't mean they don't change anything. With Patch 4 they reanimated the scene where you meet Minthara for the first time, for example. That also costs money, and I didn't see anyone ask for that, specifically, either. They are not done adding things, yet. Does this mean they will give us what we want? Not necessarily. But I see no reason to be all doom and gloom about it.
Because it's just too out of place for her to be the only one that can be turned. She was not origin for a long time, which is why I think she was planned to be "dedicated mindflayer" because the fix was never planned and cuts had nothing to do with that. For example, Astarion's content was moved from upper to lower city, why couldn't they do the same for Karlach? She barely has any content in two previous acts, if something that would affect her story was planned for upper city, it wouldn't be much and moving it would be far easier than Astarion's. That's why I think if anything is to be changed, they'll have to rewrite her. Because they didn't plan her to fixable, now the question is whether or not they'll listen
