When Bitcoin reaches that value the USD wont be needed for anything in the world anymore. 
Alternatives such as Bitcoin are necessitated because the US Dollar is becoming worthless. Soon it will be worth even less than the paper on which it is printed. Obama and Bernanke are printing more and more bills, like a competition is going out there.
If Bitcoin can beat the other alternatives, it will become mainstream.... else.....
I doubt it'll become worthless, but they certainly have the means to do it.