Last night the Greek PM took the world by surprise; he has announced a referendum on the new help deal for Greece. Logic would tell us that given the choice between getting money and struggling along or getting no money and be hungry the Greeks can only vote yes. But, this is Greece and logic has no place there it seems. So it could very well be that the Greeks vote no. A Greek no vote would mean that there is no reason any longer for the other EU states to put any effort in saving Greece from default. It could mean that they push forward leaving Greece behind (which I would consider) the positive reaction to a Greek no. The alternative is of a sort that I can't really imagine, but includes the word 'Depression'.
For the Greeks the ensuing disorderly default would mean an immediate collapse of their banking system. Banks will run out of cash in a matter of hours. People will try to pull their money out of Greece as fast as they can in order to avoid a severe downgrading of the value of their property. Greece will need that money to stay in the country and probably will impose controls. That is against the basic rules of the EU and it means most likely that Greece can't stay a member (lest it will be dragged in front of court by people demanding damages for which the state would be liable). Then they'll HAVE to re-introduce a national currency that probably will start off on a 1:1 exchange rate, after which it will plummet to depths unknown.
Of course, what I wrote above may not come about because the majority of Greeks are mad as hell with the fact that Greek civil servants have tenure even when that means it drives the Greek economy into the ground. And a referendum could effectively put an end to that.

