That also means no more bailouts for them and a default on their debt. Its going to be even harder for Greek government to pay for any social programs if that happens. Greece needs the EU far more the EU needs Greece, I bet many in the EU would happy to cut Greece loose.
Greece is not in an position of strength at moment, they are not in a position to dictate terms to other EU countries who will want the money they lend to Greece back and I don't think going it alone would help them that much. If Greece doesn't think things can get worse, they are sadly mistaken. If they leave the EU, things would get worse for their economy, not better.