People survived crucifixion sometimes. Others took up to nine days to die. Jesus was crucified on Friday, so he would have to have been cut down by the evening anyway, as Jewish law forbid the leaving of people on the cross on the sabbath (Saturday).
This is one of those anthropomorphic things. If he had died, we'd never have heard any more of him. If he survived, the whole of Christianity is based on a misconception. If he really died, went to heaven and returned - that's where faith comes in.
