What rate of descent would kill you?
There is no descent rate that would directly kill you or make you pass out, the notion is nonsense from a physics standpoint. It may be possible to rupture eardrums from the pressure change in some people with pre-existing sinus and ear trouble. It would also be possible to die from the heat of air speeds over mach 2, but the exact speed depends greatly on the aircraft design and is not unique to a descent trajectory.