All cash and currency disappear, except there’ll always be a ‘black market’ for it.
Not if TPTB deem “cash” as “illegal” or “best used by” with an “expiration date”.
Turn in your cash by such-and-such date or your bank will not be allowed to accept it.
On that day, cash dies. No one will take it because it will have no real value (since it can’t be banked)
Of course, for this to happen, the digital currency would have to be fully-operational - so I don’t expect this to happen tomorrow.
But with many governments around the world going for “digital currency” that’s my guess on how it will be implemented.
Cash will be illegal - you know, to stop illegal drugs, human trafficking, and terrorism......that’s what the nooz will say. /shiny side out