Also, in 2010 their import is 44.9 billion dollars twice the amount they export, 21.1 billion. Even if their exports go up because of weaker currency, the pain from higher import prices will be much worse than the rises of income in the short run.
Your consequence number 1: trade barrier is an interesting possibility, but 2: the collapse of EU is unlikely to happen given that the Greek economy is only 3% of EU, and this strong measure will have threatened other troubled economies enough they will be much less likely to default and cause more issues. The measure might in fact prevent the collapse of EU at least in the short- to medium- term.