Not sure this holds either. With such a black swan event, there would be a glut of second hand graphics cards on ebay etc.

Seems safer to me (if you're worried about a huge crash) to leave your principle investment equivalent amount on a good exchange with fiat support (e.g. Bitstamp) setup a sensible stop loss order and then, as soon as you've x2 your original investment, pull your initial stake out and leave the rest in crypto (on a Nano Ledger S or similar).

I think people are going to be increasingly wary of second hand graphics cards. How many of them will have been trashed by running in a poorly-cooled mining rig for months on end?

What could cause such an event? Would coinbase going insolvent cause everything to crash beyond repair?

What if satoshi appeared and dumped his entire stake? That is probably the worst case scenario I can think of.