If Jesus came back to life it would be the best possible evidence for the Christian fundamentalist's thesis
But would they recognize him?
Hypothetically, of course, if Jesus came back and told us that the religion founded on him was false, and that everyone should convert to Islam, for instance, because that was the true word of God... Do you think Christians would accept that? I rather think not.
Jesus would only be accepted in so far as he fulfilled the expectations Christians have of his return. If he deviated from that I think it more likely that Christians would turn away from him than from their own beliefs. Such is the nature of religion.