There's a slightly more modern instance of someone surviving a CuNim under canopy: Ewa Wisnierska (and some other pilots) encountered the mother of all cloud suck during practice for 2007 paragliding world championships in Manilla, Australia. Ewa survived after reaching an altitude of 32600 feet, ostensibly because her unconscious body slumped in a position that steered her glider out of the storm by weight shift, and the accumulated ice in the canopy (paragliders are a ram-air airfoil of non-porous construction) caused a collapse which returned her to a survivable altitude. Another pilot, He Zhongpin, died after being struck by lightning in the same system.
There's a documentary called Miracle in the Storm which details Ewa's survival.