If Greece went back to the drachma, the impact on the banking system would be catastrophic, in my opinion. Who would Greek banks borrow from, and how would they get any deposits? Gresham’s law dictates that people will be saving in euros and will be transacting in drachmas, at least outside of black markets. The euros will be hoarded or will be deposited to other European banks. Who in his right mind would be depositing euros in Greek banks if a mandatory conversion to drachmas could not be ruled out completely?