True, but you can easily have a currency union without political union. For example, many countries use the US dollar or peg to the US dollar.

Greece could stay in the Eurozone, but the Greek government could default on its debt repayments. Of course, no-one would lend any more money to the Greek government. The government would immediately have to start spending within its means, and is that a bad thing?

But this crisis isn't about that. This crisis is about finding ways to keep Europe chugging along without exposing the folly of exponentially-increasing government debt.