it's highly unlikely that one currency will be used internationally, what is more likely in my opinion, is that several thousands of additional (virtual) coins will be added and used by people. That has the benefit that a crisis wouldn't have a huge effect internationally, since things are not that interconnected anymore
It is likely going to happen as many theories that bitcoin will be used worldwide so it's essential that it will be used as world currency. Besides, there are conspiracies that bitcoin will be the one to use for the one world gov't currency and it's the currency that will be used for the cashless society, I'm lack of ideas with this but there's a possibility it will happen.