Exept if Taishakuten's in Celes, maybe Kujaku's there too, and god, can't you just imagine Fai and Kujaku bouncing around driving Kurogane crazy?
If there's one character I can ask CLAMP to show in TRC, it would be Kujaku. Pity Fai and Kujaku don't look alike, else they make very matching brothers.
However much I wish its true, its unlikely that Taishakuten is in Celes (alive and well, at least). Cause if thats the case, (as suzine has pointed out) he would be in Ashura-ou's side , and Fai should be more scared of
him. I fangirl the man, but he's a bit obsessive when it comes to Ashura-ou. I doubt he would take Fai sealing Ashura-ou well.
As for whose fault it is, I think both Ashura-ou and Fai are not completely innocent, so you can't really put the blame on one side. I don't think Fai is traitorous, so 'betray' doesn't seem to be the right word you know? Ashura-ou can also be considered very selfish in Rg Veda. Fei Wong might have meddled too. In the end, its probably everybody's fault.
I'm waiting for the 'Fei Wong discussion' between Fai-Kurogane-real!Syaoran, Clamp. No more distractions, you hear me (as nice the fanservice is...)?