I think the only way to redeem him is to cure him of vampirism, maybe he doesnt even need a redemption, just a change of heart, I feel like his story is rooted towards Cazador and whatever happens with him will obviously effect the outcome of how Astarion will be in future.
I just have a feeling because we are given either the "heroic" or "villan" option regarding the party, we will have more options like that in future, and it will have a major impact on the companions and their outlook at the end
Astarion says we can just kill his master or he can become a coven leader if he drinks blood. I think the second option is evil. I don't know what happens to a vampire if someone kill hes leader's. hm… Maybe this is a "good" option.
