Vendak clearly said a shot through the head, a shot through the head at that angle is a 100% chance of death. You would have to shoot at a different angle (thereofre botching it) for it to not be a 101% of death
The chance is actually zero. The combustion of the bullet itself alongside the action of the handgun is enough to dislocate/break the jaw and shatter the back of the skull/tip of the spine. The bullet itself would rip through the brain and the nervous system. The ONLY way someone could survive is if they botched it and aimed low and it exited below the back of the skull, however this would still cause near fatal injuries and would still wreck the spinal cord, resulting in probabal death anyway.
Also that video was JFK's assination, he was shot with a rifle albeit, which is a far heavier and faster round, but given the distance similar physics can be applied to a handgun at point blank.