>Update: I think the direct answer to your stated question would be yes, a priest will change his belief assuming (a) the man is rational and not delusional, and (b) the proof is truly beyond doubt.
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>I'd be surprised if that were the case. (Of course, it's a hypothetical question). Priests are not stupid - they know that the minute God is "proven", the game changes for them, and they can no longer play it "deuces wild". Proof of God would likely wreck religion.

In one of Graham Greene's novels, "Monsignor Quixote", a priest has a terrible dream. In the dream Christ returns to earth and proves beyond the shadow of a doubt that he is the son of God, a deity. The priest says he felt like he had lost his reason for existence.

I don't happen to have faith but I think it's a very cool concept. Much cooler than knowledge in some ways.