My guess is that you may have burned it under his belly. If he hung up at 40 yards he may have guts herniating. Fatal for sure and he wont likely go far before laying back down. I would say that if you cant find ant blood or other sign, a tedious grid search of the standing corn ought to find him. Don't beat yourself up over it. It happens to all of us if we've been bowhunting long enough.