If Greece really do decide to leave EU (which I doubt, they aren't stubborn and vengeful like Russians, they are more of the asslicker, easy life kind of people), then we are all in deep shit because already weak Euro is about to get worthless sometimes next year and Greece leaving the ship (and suiciding in the process) will have effects on that and get Euro to historical low compared to USD. My salary isn't tied to Euro, but prices of everything are and that will mean life is going to get even more expensive than it already is. At this point I really wish Serbia was some kind of USA colony, rather than potential EU candidate.
Also that would make a precedent and open possible scenario for exit of other economically weak southern countries, which would bring EU once again to its core and that isn't big, huge country they envisioned it to become. Not to mention that further expansion will completely stop.