If Greece decides its time to move back to the Drachma so they can implement some monetary easing, devalue the new Drachma and pay off their debts with this cheap money.
Will it be this simple?
How And When Greece Will Leave The Euro; New Drachma To Slide 50%
With the tide turning against a Greek unity government that will respect prior agreements with the troika, the possibility of a Eurozone breakup is no longer just an academic possibility. The consensus is gradually accepting a Greek exit as a likely scenario: external funding could dry up, severely constraining the supply of euros and leading to the adoption of a new currency. According to Nomura, these neo-drachmas would face a 50% to 60% depreciation, while the euro would tank, falling to 1.15 to 1.20 against the U.S. dollar. This is why it could happen, and how it would go down.
The cards are stacked against the least dangerous scenario, Greek permanence in the European Monetary Union. Rising Greek political star Alexis Tsipras, head of the far-left Syriza party, has walked out on talks to form a unity government with the more moderate PASOK and New Democracy parties.