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.
You are right, when after greece another country will left the euro than its over.
But it will be a new beginning, every country will choose again his currency,
it will be the best way in my opinion like it 15 years ago was in europe.