Well.  Its really up in the air isn't it?  I don't see it happening.  Bigger, broader currencies are becoming much more common.  Libya, prior to the middle eastern uprising, began an African central banking system,  some countries in South America (Brazil I believe) has expressed the desire to have a continental currency.  The bottom line is this: with the world becoming more and more connected by the day, I don't see the economy running much differently.  But at the same time it is a terrible step!

 

Many have said that the true failure of the Euro is the fact that it has no single governing body.  Where the Fed and the USD has the US Government to "monitor" (and I use that term very, very, very loosely) it, the Euro has too many countries and governments wrapped up in it.  Countries like Greece are on the outskirts of the euro zone and cannot handle such a monetary system...hence Greece's economic decline.  It has nothing to do with Greeks being lazy or any of that bull.  Goldman Sachs transitioned them into the Euro knowing that would fail with it.  This ultimately put Greece at the whim of the modern, western capitalist system.  Seeing that Greece has all but admitted its being in a debt trap, I think most of this holds true.  We "conquered" Greece.

 

Also, educated economists and government players know of the instability of large currencies like the Euro.  If they are used to bring about instability, then a strong world cohesion of governance is needed to combat forced global economic failure, and then we start hearing statements claiming that "world cooperation is needed to [fix] the economy" by institutions such as the IMF.  Basically global failure brings about global cohesion.