In theory, Greece could exit the Euro if it has a primary surplus. Which it does since earlier this year. However... Greek statistics are back: Primary deficit presented as surplus, with Eurostat's seal of approval (April 24, 2014)

Eurostat has just approved the Greek statistical service's (ELSTAT) figures on the general government's primary surplus of around 0.8% of GDP. Were that true, it would have been of great significance. Not because Greek debt would have, magically, become sustainable but, rather, because it would have meant that the Greek government would have acquired great leverage in its negotiations on the impending restructuring of Greece's public debt. Put simply, it would mean that the government could, at least in theory, suspend debt repayments to the troika while the negotiations are continuing , without having to renege on its payments of salaries, pensions, and suppliers. Alas, the Greek government's 2013 primary surplus is a statistical mirage. Moreover, it is a mirage purposely concocted by Eurostat and ELSTAT under the watchful, and conniving, eyes of Berlin, Frankfurt and Brussels. Mindful of how weighty these charges are, I list my evidence immediately below.

A society committed to the notion that government is always bad will have bad government. And it doesn't have to be that way. — Paul Krugman