According to the treaties, there is no way for a country to exit the eurozone. It can only leave the EU as a whole.
Even if a way is created, then Greece has a WMD to put in negotiations. Leaving the EU as a whole.
The implications under a geopolitical scope would be huge for Europe. There would be no border continuity to SouthEast Mediterranean and the new discovered Gas Fields which are vital for Europes energy independence. Who always have the Russians, that would give a lot for the passage to the Med too.
I would be very interested in your views on GrExit under the geopolitical scope.