I'm just wondering how far you have to fall to break your neck and die.

This is the scenario: Man A is standing with his hands stretched above his hands and Woman B is doing a hand stand on his palms (kind like circus trickery/Cirque du Soleil stuff). I'm just wondering if he takes a step back, or they're unbalanced for whatever reason, if she falls and lands on her head, if that would be enough to kill her.

(He's six feet, standing, plus whatever reach his hands would have above his head).