A Greek default has no impact on the Euro. A Greek default will drill the French and German banks that hold their debt. That's the issue.
The penalties of defaulting are probably already negotiated to far outweigh the penalty of stark austerity measures.
Moreover, the SPV and the bailout plans in the eu seem to be more like smoke and mirrors than concrete stuff (e.g. bailing out greece with money coming from portugal which is in the same position)