So Rag, your response does make me think more about what they are trying to convey about Astarion's character. I think your'e right that his characterization is actually quite consistent overall. My big problems are I think two-fold. The first is that while Astarion's characterization is solid and kinda interesting, the more it goes, the more it feels like they're not making a companion, they're making an antagonist. At this point it feels like the natural way Astarion's plot would develop is that if you get the bitten to death scene, then Astarion flees or you drive him away (glad to hear there's an option to drive him away) and he eventually comes back later as an outright antagonist out for revenge because he feels you wronged him. And that would be a super interesting. But Astarion as a companion character? A character we're supposed to bring along and be interested in keeping around as players? They're giving us too many reasons to want to kill him and not enough reasons to want to keep him around. I'm not even talking about making him nicer, just making him feel worth keeping in-story. I don't think the game gives us much in-character reason to keep him around beyond "strength in numbers." As bad as Shadowheart might have been at first, I don't believe she ever actually tried to kill us. That they felt it worth changing her demeanor and not Astarion's really says something. I don't know what, but something.
My other problem is that this scene feels like not just Astarion but the game itself disrespecting the player. Maybe I'm just sensitive, that could certainly be true, but it feels like the game is outright insulting my character through Astarion. A feeling that's only amplified by how little the game seems to regard player-made characters in general.
Wormerine, I think your point is a really good one and it's why I think this should just have been a game over. I think him killing us works as a kind of easter egg joke ending, a ha-ha, this is what you get for trusting the evil vampire type thing. But not only does letting the game continue on muddle the worldbuilding by making resurection a direct part of the in-canon story as opposed to something that's mainly just a game mechanic, but it puts the player in a situation where the only options are eject Astarion or be as much of a rube as he clearly thinks we are and let him get off without consequence.