There has been a lot of discission effort putting into lamenting the fact that many of the companions do not have what people think would be happy endings. I want, for a just this discussion to consider from a game world development point of the view, happy endings might not be the best idea.
By not closing loop holes, by leaving things hanging, Larian's story writings have left some AMAZING future game/adventure pack hooks in place to let this story go forward. For example, Karlach and Wyll are in Avernus, this allows them to easily be hooking into a future product where you travel to Avernus to save one or both. Or even just an adventure into Avernus where you encounter them and perhaps they help you.
What about Asterion? Well if he did not become the super evil vampire, maybe in the future you could have a chance to rescue him, cure him even. Or perhaps he himself becomes the hook, reaching out through his contacts at Baldur's Gate for adventurers to stop an evil vampire plot. By leaving things a bit hanging we have easy to implement plot potential.
I feel like the reason so many people are upset about the various endings comes down to two things. First Larian made you care about the companions in question. This is a testament to the great storytelling and voice acting we see in the game and should be applauded. For people to care this deeply about an NPC companion is actually not a common thing.
The second reason is they see this game as the end. The story stops when the credits role. I get it, that is the way a lot of games work today. However I am "hopeful" that Larian loves the ideas od DnD as much as many of us and those of us with a deep DnD (or any well done table top RPG) background know that loose threads, unresolved situations, often lead to entire new adventures.
Is this Larian's intent, I have no idea. I can hope, and as long as those threads are hanging there is a chance for that hope to live. Once you tie up everything in a neat bow with happy endings all around that hope however withers. Happy endings mean adventurers are content and moving on to normal lives. The deep hooks for the GM to use to draw us in vanish and if they try to create them, they become forced.
A happy ending for our favorite NPC would be nice it would give us a warm glow and closure. However by leaving things as they are, maybe, just maybe, we have a chancing of continuing the story and seeing this beloved NPC again.
