Short-term:
So what are these last resort plans?
Obviously, even if the idea of the Eurozone fails, foreign bond holders know where their bonds came from. And they get converted. The "crash" does not mean that trillions of Euros would be suddenly totally devoid of value.

Why would Germany print Deutschmarks? It would cost them a lot. My guess is that the countries on the same level will stick to their euro and all those may be swept out before the end of the year that cannot handle it.

LONG-TERM:
At another level, many here remarked on the utter insanity of the whole present financial system. It makes me wonder why central banks are freed from their own democratic legislatures ... while the country they represent cannot inflate if they choose so. At least capitalism worked better before monetarism and fundamentalist free market policies. This could go on as above for a while. But what happens if, say, France gets suddenly richer and wants more money circulated than Germany? They still have to agree with all the other remaining members.

It would be far easier to have a really joined EUS which could then invite countries one by one to join.
It was the lack of real economic help and restructuring - as well as the corruption of their own rich classes that made the toeing the line by the newly joined Eastern European states impossible. In fact, the Eurocrats demand a stricter balance on Hungary for example than on their own core countries. Look at the targeted GDP/State Debt ratio of Germany, France and Hungary for 2012. Well. Maybe Hungary for example would better join some Eastern European entity to be created in the future from all those disaffected by European policies.

Britain will always be isolated. Guys, this has long roots! It is an ISLAND after all!
(OK, I know so is Ireland but the Irish want to cross the, at every opportunity.)