I really want to know that, if all the United Nation members leaader are agree to accept bitcoin to use as an official currency for International Trading replacing US Dollar, is it possible to happen? and if it is really happen, and then what happen to the price of bitcoin?
you should instead ask "why would they even consider doing this?"
it is an impossible thing to happen unless there is a damn good reason for it. right now there is no reason for abandoning USD, it is working fine and it is easily accepted anywhere with the price not fluctuating that much. and if there was a reason for abandoning it, there is still EUR.
and as long as these are working fine for the nations they won't look for an alternative that has a volatile price and is not yet mass adopted.