that's not going to happen anytime soon. the value of the US dollar is backed up by something a LOT more solid than gold: worldwide demand for geostrategic resources. If you are Japan and you want to grow your economy you need oil, steel, grain, sugar, etc...and guess where are these all traded and in what currency?! If you produce these and try to set up an alternative market to sell them, you'll get bombed! So, no, this whole talk about the US government going "bankrupt" is just supply side propaganda. They want people to believe that the private individuals who hold the US debt and charge an interest on it are not under the protection and control of the US elites. In fact Wall Street is the single most important creditor to the USA. US taxpayers paying an unconstitutional tax to private US citizens and non government entities such as investment banks by simply paying the interest on the national debt.
Contrast the right wing reactionary US system to Norway's socialist Kroner which is backed by stocks from the largest corporations and sovereign papers (treasury notes) in the world as opposed to resource monopolies. So when the world economy grows 5%, their treasury growth with it. The only way to bring that currency down is to bankrupt every single company and government in the world. Not likely anytime soon. so the world is literally paying for Norway's socialist welfare state by simply prospering, which I thought was very cool.
http://www.articlesbase.com/finance-articles/the-safest-currency-of-the-word-at-the-moment-the-norwegian-kroner-833101.html