How about a backup bank for each exchange?
How difficult would it be to ALWAYS have at least two bank accounts for an exchange, and when one gives notice of closure, move all the fiat into another one, then open a new account with a new bank (if you want to continue operating)?
The number of banks is of course finite, but given how many credit unions and similar banking services are there, it seems like this strategy would allow an exchange to survive for a pretty long while.
How come this has never been discussed?