Cash is King - and Greece
The Greek referendum will be an interesting exercise. At some point the Greek government runs out of cash. After that point no-one gets paid. I suppose they can start by holding back on big payments, but after a point salaries are not paid, pensions are not paid, suppliers are not paid.
Cash becomes "king" because no-one will give the government any credit unless they are forced to.
The government could print a "new drachma", but I am not sure what that would be exchangeable into.
They cannot simply refuse to pay the outstanding debt because the other countries would not accept that and they cannot isolate themselves.
If they are going to hold a referendum they will need to do this quickly.