FR actually isn't the problem here -- in fact there is an exploit in the game that could eliminate his vampirism. Kill him, use Gale's scroll of true resurrection, and if Astarian wants to come back the taint from his soul is cleansed. In the original Raveloft module this was one of the possible endings. You could use true resurrection to liberate Strahd's soul.
But this is exactly what I meant when I said it is a problem... it's no redemption if all you have to do to attain it is some technical magic. The problem is that as long as Astarion is a vampire he can't have redemption, he can only have some sort of redemption forced on him. any redemption of that kind is not really a character arc but more of a side quest.
