I am not too fond of giving a good ending to every companions just because some people got too emotionally attached to a virtual character. Having a doomed character can be a thrilling element in a story, see Cyberpunk for a recent exemple. I admit that Karlach story isn't good in that regard though. The only conversation about how doomed she is is put under the rug for the rest of the story until the very end. Larian probably wanted to show how optimistic and carefree this character is, but forgot that this plot point is a core component of her. So people are dumbfounded to find that this unavoidable conflict eventually get "resolved" in the last few minutes of the game. Meanwhile, Astarion reminds us constantly of his condition and his goal. His story feels way more organic because it isn't a big void of nothing until players get hit by it.
That's a way different case, as Cyberpunk is a more linear game that led to 3 different way to start the last mission, depending if you choose to be who you are, to let Johnny take the lead, or to doom the whole world. Plus you know at the beginning of the game that you're condamned.
Here the problem is, game gives you a problem, provides tons of solutions... but never let you try any solutions. There's two different notions : - Having a doomed character whatever you try - Having a doomed character because the game doesn't let you try
Karlach is in the second case. It's like the game tells you "hey here's a solution for Karlach, look at this big ol' forge, look at all these metal, look at those Gondians that worked on a similar prototype", but never let you talk to them, try a subquest where they could work on a fix. If the game was linear, well it is what it is... But damn this is a RPG with 17,000 ends, we can expect way better than a single dead end you have no choice but to take.
I can expect that if I do everything correct for Karlach with all the ingredients the game gives me all along my play, I'll have a good ending. Like any other RPG, like in real life. And if I miss something, for example here if Dammon dies, or if I don't free the gondians, or if they're killed, without even considering talking to Mizora... well in that case I assume I'll have a bad end and Karlach will have to go back to Avernus.
And if they absolutely want to bittersweet Karlach by not solving her problem in-game (which is not an obligation to always have a doomed character in a game, especially in the Forgotten Realms world where everything is possible but anyway), so we can easily imagine a last mission where you talk to the Gondians, give them all the ingredients and they tells you "I've never seen that kind of mechanic/magic before. This is not supposed to be in that Existence Plan. I prefer not to try to repair it as it could explode instantly. You'll certainly have to go back to Avernus". Like that you explore all the options, you have the feeling you did everything you could, there's no solution here and right now, but you have an epilogue that explain the follow.
There are plenty of better work doable with Karlach, and the game uses maybe 10% of what this character story can be, while any other companion are mostly well exploited. In my opinion, The Ancient Forge was initially dedicated to Karlach story. This is not useful for the plot at all, we could easily had a direct path from the undergrounds to the Shadows. Why do we have to explore this forge ? Why is it so detailed when it's absolutely useless in the main plot ? But they had to cut some quests to release the game.
Craziest part is that its not even the Gondians working on a similar prototype, they created the stable version based on hers. They are entirely capable of solving the issue.
