If all the exchanges lock users out, you can “transact” with BTC But can you convert it into US dollars? Where does one spend BTC these days, buy some furniture off overstock?
Pawn shop? Or maybe at a supervillain's lair, where sellers are known to accept briefcases full of gold.
Usually you need to convert your gold to a legal tender currency in order to be able to spend it. You normally lose money on the conversion at a retail volume, though.