steveo say
So what happens to the "excess euros" that get abandoned by these weaker states, they also rocket up in value?
I think your basic premise the Euro is a weighted average of some phantom equivalent FX value is just wrong. There isn't any phantom equivalent currency. From a mathematical point of view I see the beauty of that as a simple equation, but I see no reason to think that it is true.
Counter-intuitive I know, but the fact is that the weaker member states leaving the euro effectively makes the euro the Deutschmark, which is worth more usd.
You will incur heavy losses betting against the euro. It can and will appreciate against the usd as weaker member states leave.