First and foremost, cash balances at coinbase are FDIC insured.[1] There are regulatory requirements for cash on hand because of this. In the worst case, the FDIC should step in and fork over the cash that people are trying to withdraw.

Secondly, the drop in price of crypto shouldn't cause something like this. Coinbase is a marketplace. When one person sells their cyrpto for fiat another person is trading their fiat for crypto. When someone is going to withdraw money this transaction has already taken place.

1. https://support.coinbase.com/customer/portal/articles/166237...