Personally, I would elect to let him lay. I would rather find the deer the next day, rotten meat/eaten by coyotes, than not find him at all. At least you have a sense of closure to the story, and are not left second-guessing your decisions and having to live with a deer that was hit and not recovered. That sucks.

EDIT - I don't think there's necessary a right or wrong decision in this case, it's up to the individual who shot the deer. If you are that concerned about spoilage or predators and decide to go chase the deer, that is your perogative. You may find him dead, you may bump him, or you may not find him at all. Those are the chances we all take every time we let an arrow fly.