Having the entire reserve as cash wouldn't exactly help here - imagine if 30% of USDC's total reserves was in Silicon Valley Bank, rather than just 30% of their cash. (I think I've pointed out before in discussions of Tether etc that stablecoins can't safely just hold their rexerves as cash in a bank account because banks can and do fail and FDIC protection basically does nothing at this scale, but I wasn't expecting it to be demonstrated quite so spectacularly.)