Then Bitcoin or any other crypto currency by then would probably have too little to no value at all. People who still owns them would only probably see them as collectibles that hold historical value because having such a scenario happen would mean that the whole world is already on its worse state. Meaning, the only thing that would probably be used to get services, things or food would be trading for whatever each party needs, like basic necessities, services or whatever. And if ever, people would rather utilize gold, silver and any other valuable natural resources more rather than crypto.