Agreed that the party scene was a great subversion of expectations. I'm still hoping that there is redemption path but it is getting harder and harder see. His reaction to return of Connor was the turning point for me -- this was just mopey, "that which defined my life is gone now I don't know what make me happy" Astarian. This was someone who delighted in cruelty. And it seems he wasn't a good person before becoming a vampire. Redemption, if possible, will hard path to follow.
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.