One economist I follow predicted 4-5 years ago that the US and EU's currency would collapse (as well as many other countries in the world). What would happen is that a) new currencies would be created on a country level (i.e. a new US dollar and a new German deutsche mark) BUT...these currencies would ONLY be used locally (i.e. not internationally). A secondary, global currency would be created which would facilitate international trade. So you might have 2 US dollars (the local, US dollar and the international version) and 2 German marks.
There is no way that this global economic catastrophe ends without a global currency in some form - that's the entire purpose of the planned catastrophe. So a 2-tier system for each country makes sense. Time will tell...