Credit Card companies and banks can reverse the transactions, so long as they keep track of things in batches, have strong backup system for their ledgers. So long as they're not SWIFT transactions that leave the country, and the country that's attacked as a strong/regulated inter-bank transfer system.

If a bank is critically hit so bad funds become impossible to correctly attribute to people (Fight Club type unrealistic scenario), at least in the US FDIC would probably come in to play. The bank might even have to be treated as a failed bank.

People wouldn't stop using banks, but they would stop using that bank.

Neither of those things "are money" and they're all highly reversible.

A major hack against Visa would absolutely tank the value of Visa the company however, and if people who believed they were paid weren't made whole somehow then it would also tank the acceptance of Visa.

And it would be an ongoing devaluation without Visa being able to show they'd fixed the underlying flaw - which you can't with a 51% attack.

My credit card gets stolen yearly. Sure, they can reverse the charges but changing the number everywhere is annoying..