If this happens it will be a few generations (at least) from now and when that happens ppl will look for something to get around "the system" much like ppl are doing now with Bitcoin.
I'd expect gold, and maybe silver, to become that physical currency and be worth more than ever imagined. Something similar to an underground/black-market type of scenario I suspect.

As history has shown since the beginning of time, ppl always find a way.