Well maybe im Wrong but for Me Astarion should Never Had a Good ending.. he is a Thief and a Vampire.. theres no GOOD in him.. i all my games when i was playing a good dude by the time i get to finish his quest when i refuse to help him becouse i will not create another moster im a hero.. he just made me kill him.. i Beleave that He never was supposed to be played as a Good Guy like a Said.. he is a Vampire and a Thief.. dude in Any tabletop he at least would have been a Neutral evil..meaning he was never supposed to be GOOD. But ho knows maybe im Wrong and yu guys are corret.. i just always felt that he is a Companion Perfect for a Durge game or a Evil one becouse in all my evil games he basicly become my right arm man and minthara my Demonic Godess. RS and Fun Fact He was like a Devil in my shoulder the entire game like in old Cartoons.. haha
Pretty much sums up my thoughts also. My Tav was always keeping an eye on him to prevent him being trouble; I recruited him for his probable usefulness in BG since he had connections there. Once I resolved his quest by killing Cazador sans Astarion (and all the Vampire spawns) I killed Astarion. He is too dangerous to keep alive.