I'd say that there'd always be a form of currency like "cash in hand" that would facilitate face to face transactions that leave no record of the transaction save in the memories of the participants. Even the privacy that could be realized with crypto will not entirely remove the want for an exchange of goods/services for a tangible object with accepted value(i.e. gold, cash, food). I feel that the black market, despite  SilkRoad and other darknet sites, will continue to move largely in this way.
I find it a source of unending irony when bankers/governments cry foul on BTC and crypto for being a haven for black market trade and terrorism when it's painfully obvious that it is USD, which is by far the biggest currency used by criminals and terrorists. You want something illegal? Best have some USD handy, it'll get you whatever you want. My two satoshi worth, if even that...