I agree, you have a point, Larians need to add more content for it, expand the questline, but not change the ending. You just can't save everyone, you always have to sacrifice someone and i like it, like the Tieflings if you choose Minthara or Balduran if you follow the Lae'zel storyline and free Orpheus.
And that's great that you like it! I think at the very least most of us here agree that what's already in the game should stay in the game, but it does (ideally) need to be built upon. However, for me and many others it's often like... "You can't save everyone" - well, why can't I? If you (as in, the plot) are going to tell me that, give me a reason better than "because I said so".
As you yourself said and as aoife pointed out, tieflings/Halsin vs. Minthara and Balduran vs. Orpheus are choices. There's a clear answer there - "You can't save everyone, because these things here are mutually exclusive, it's either or". I have no qualms with that.
There's no "either/or" in Karlach's case. There's also no "Here, try all these options and see for yourself that none of them help" thing going on there.
So like. Until there's a clear "You may try, but in the end it's pointless" debunking of the already-in-game options we may try, I and many others will remain feeling like it was possible, we were just not allowed to try. And for as long as we feel like we could've tried harder and weren't allowed to, we will believe that IF we could try, we could help her (nothing says otherwise, after all). To that end, a happier ending remains tangible. There are two solutions to that - either we're right and it is achievable, and then adding new content will let us help her, or the writers are adamant on the tragedy they've written, but then they'll need to convince us that we really, really, REALLY couldn't help. It will suck, but at least it will feel final.
Well, that, or they don't change a thing, of course, but that's another matter entirely.
OR, as per example with Minthara and Orpheus, helping Karlach might be a possibility BUT it involves some harsh choice with strong enough consequences that players may consider not to. Or it is tied to some quest or event or a trial that's easy to fail. So that when the tragic ending comes, it actually does feel like, well. You can't save everybody.
(although in that case I already have one fictional city destroyed for one girl's life under my belt, don't try me)
![[Linked Image from tarraxahum.neocities.org]](https://tarraxahum.neocities.org/buttons/2rdo1pL.png)
