I think you don't need to worry about it, because the Fiat will not dead, the government will not let him during their there, and is not possible bitcoin will be adopted enough to overthrow the government's great. the same as we have paper money supported by gold in the past, we might get Bank will publish note supported by bitcoin in the future, and they will be easily prove that they are holding the coins with just shows their address and signed message. bitcoin physical this can then be used in places without Internet access. of course it will not be safe and unreliable like bitcoin true, but still it is the solution.