If he went under the chin, it's going to probably blow off most of his jaw/tongue/nose/eyes. Major neuropathy, possible blindness, loss of taste/smell/speech, maybe eating if not breathing through a tube. If he shot from the side and it just went too forward, the frontal lobe is the person part of the brain that's scrambled with lobotomies. You just lose your personality, executive function/impulse control, muscular control, and learning/memory. Either way his quality of life is probably going to plummet without anything more than cosmetic solutions available.