If you haven't found him using a few friends going in the general direction he was headed try to see if the slug came out of the deer a rib shot with a 12 gauge at that range should have been through and through. If you find the slug see if the the area around it has spray. If there is no spray at all there is a good chance that you missed him. But you owe it to the deer not to give up on assumptions, you either know you hit or know that you missed him.