Since leaving the Euro would be equivalent to a sovereign default anyway (and treated as such by the markets), and would have much worse additional downsides, what incentive would they have to do it? IMO it's a very slim chance, any independent Irish or Greek currency would be crucified immediately after Euro exit, and throw the countries into economic chaos.
This reminds me of all those people who kept shorting Eurolira and BTPs against Euribor and Bunds, all the way up to monetary union, on the basis that the EMU/Euro would "collapse" or countries like Italy, Greece, Spain wouldn't qualify. Those speculators were simply clueless about the political realities of Europe at the time. IMHO the EU would always bail out a fringe country rather than see one exit and endanger the whole European project, and no fringe country would exit the Euro for economic reasons alone.
