I suspect a seat belt in this case would have killed him. He free-flew out the front windshield lowering the otherwise high-g sudden stop. Of course, predicting beforehand which effect is more deadly is impossible.
hmmmm ya might want to think that through a little. There is a little "give" in a seat belt and the airbags work on the deceleration. That is unless you put your feet on the dash, unbuckle and decide to let the ground outside....like say concrete.. that doesn't budge a inch stop you. hahahahahahahaa...... That guy BOUNCED after he hit the ground while flying through the air with the greatest of ease.
What saved the other 4 people in the car?