The government would have planned and figured this all out ahead of any action they might take if they were intent on looting bank deposits. If they were to declare a bank "holiday" and close them from desperate depositors trying to get their money out, while at the same time calling in all dollar currency and issuing new currency, it could happen literally overnight. Having cash-in-hand might might not be a benefit at all, if the cash is no longer considered good currency. Who would take worthless paper in exchange for something, when they wouldn't be able to spend it themselves?
The fact of the matter is, none of us know what will happen in the future anymore than anybody else does if the world burns to a crisp. I was just expressing my opinion on what might happen.
Merry Christmas.