Indeed, and that will happen sooner than people expect. Unemployment is going to increase and many people are going to be forced to sell cryptocurrencies in order to pay their bills. Imagine choosing between having a cryptocurrency portfolio and having an apartment for another month.

Exchanges are not prepared for what is coming and, as you point out ("A bitcoin-only market is essentially an exchange killer"), they cannot be prepared for what's coming.

The only reason Bitcoin could survive such a crash is because has such a higher price than all other cryptocurrencies. It's like every cryptocurrency is standing on a ladder. When the market goes down, they all step several wrungs. Bitcoin has the tallest ladder by a wide margin.