The question is, if Greece managed to leave euro, that could mean other countries which are also in debt can also follow suit and do the same. Eventually when more countries follow the same action, it can only mean that the whole union will collapse. These has been projected to happen for some time now and I see no other solution.
Maybe, in the end, that's the best solution: a collapse of the whole union. Although it's hard to say, but I think many (wealthy) countries in the EU think they should never went for the Union in the first place. Many people here in the Netherlands argue that we should have kept the Gulden instead of going for the Euro. This has huge advantages, but sure, it also has disadvantages.. I don't know what would have been the best.
And If the whole union will collapse, USA will rule on us. We really need to have a UE, with same laws, where goods can circulate without any fee. Only in that way we can improve our countries. If we come back to be single states, USA and other powers will trade only where is more convenient. The countries with higher debt will go in default and they will buy industries, societies for a bit of money. So, in my opinion if Greece go out from UE, we need to be more united to face this crysis.