I don't think the EU as in institution is quite as vulnerable as Clive reckons, but currency union is surely on its last legs.
The German Government is, rightly, refusing to accommodate the Syriza expectation of a further 50% write-down, because as Clive points out, the rest of the PIGS will immediately demand a similar accommodation. Merkel has zero room for manoeuvre on this matter, because German citizens refuse to fund (exceedingly generous) retirement plans that allow Greek citizens to put their feet-up several years ahead of their Teutonic counterparts, and equally, they should not be expected to pay for the profligacy and financial mismanagement of their Southern-European partners.
There is only one way that the Euro can survive and prosper, and that's if there is full fiscal consolidation across the zone. Unfortunately, the very strong likelihood is that sovereign European governments would find it impossible to get such a vast secession of power, past their respective electorates.
Maintaining the status-quo is, in my view, merely postponing the inevitable. The Euro would have had a chance if individual Nation-states had stuck rigidly to the rules of operation, but these were either flagrantly abused, or ignored completely, from Day One. Nationhood still matters in each of the individual jurisdictions, and the belief that Federal control and distribution along the lines practiced in the US would ever be acceptable, is/was pie-in-the-sky nonsense. The Germans simply refuse to bust their balls grafting, to fund fecklessness and idleness on the part of people with whom they have no real affiliation with or obligation to.
Currency Union has, to all intents, already failed, and I'm rapidly coming to the conclusion that the quicker it is killed-off, the better.