Really? I think more coin exchanges have fallen since bitcoin was invented than traditional banks.
Here's another happy story for coins.
https://gizmodo.com/crypto-exchange-says-it-cant-repay-190-million-to-clie-1832309454
This article for an Exchange, just because they die doesn't mean Bitcoin does.
Exchanges are essentially replacing banks, or at least acting like them.
Using your example, if a bank goes under, does the currency it transacts in also go away? No.