I'm not sure if I think Sam believes any more. He certainly seems unwilling to accept that God has any sort of plan, with the way he's been dealing with demons and such. I don't believe he's fighting demons to help people anymore. I think he's doing it because on some level he enjoys it.

For Dean--"Houses of the Holy" does end with him saying he thinks he saw God's will. I'd be inclined to think he views God in the same way my grandfather does--there is a god, but he's a sadist. I was also trying to make this point to dotfic, but I think that Dean has shown himself to be much more willing to put his trust entirely in someone else. He blindly followed his father, even when his father was just a voice on the phone. I think that his problem with Castiel is that he won't just take a supernatural being's word that they're good. But if he did ever get to that point, I think it would be a powerful draw for him to have someone else give him his mission. People have made a lot of the fact that no one ever asks Dean what he wants. I think what Dean ultimately wants is for someone else to give him a purpose.

Hmm...I seem to have muddled this...