I actually think it is. Sovereign default doesn't imply an exit from the Euro, and if the money markets close down to Greece as a result and the European System of Central Banks temporarily stops clearing payments with the Greek Central Bank they pretty much force you to issue scrip to keep functioning, institute capital controls, or other emergency measures suspending parts of the EU rules. You can always pay any fines imposed by the European Court of Justice a decade later, when the economy has recovered.

Keynesianism is intellectually hard, as evidenced by the inability of many trained economists to get it - Paul Krugman