But that's not possible. Cryptocurrencies are mostly kept as investments. People may withdraw some small sums but even then they'll sell them for fiat, which won't result in a collapse, for basically the local fiat will be bought in the end.
I think the problem mostly occurs when people take a lot of fiat and sell it for a cryptocurrency, but I doubt people would do that now, as prices are high. Thus, in fact, I think there's more threat to cryptos in the current situation rather than to fiat.