I am almost positive that the Sandor Clegane is still alive. The evidence in AFFC is pretty convincing in that regard, even if it is very subtle in typical GRRM fashion.
I don't know how big a role Sandor will have if he's become a brother/monk, but the set-up is perfect to have zombie Gregor fight for Cersei in her trial by battle, and to have the Hound fight for the church that's accusing Cersei. That fight has to happen!! Come on GRRM, don't let us down!
If you still doubt that Sandor lives, read this excellent essay on the subject (which has all the relevant book excerpts from AFFC), and then tell me if you're still convinced he's really dead:
http://towerofthehand.com/blog/2010/...he_/index.html