Only Greece and Portugal makes sense for an exit from the Euro.
Thus only bank runs in these countries make sense. They could happen without making sense, of course.


In regard to Greece, I would simply not exchange Euro for Drachme, but instead simply establish Drachme as the official currency - and send the police to close all businesses that refuse to accept Drachme.
Euro would effectively be a foreign currency, and be used accordingly (see Kosovo).

Meanwhile, the Greek state would receive all its revenues in Drachme and pay all its employees and contractors in Drachme.

Whatever state bonds the Greek banks hold (and would lose) could be compensated by the government adding equity capital to those banks on an as-needed basis. A kind of equity capital giver of last resort for one year (including an immediate re-election of the management board so current shareholders have the opportunity to make sure the management doesn't see this as a carte blanche for risk speculation).


There would basically no reason for a bank run, as the Euros in bank accounts would not lose value and the banks would have liquidity.



Impact outside Europe; see the latest Argentinian bankruptcy. Everyone got over it.


Whatever damage such a drop out of the Euro means; it has to be compared to the damage that's being done by staying in it.
The currency is awfully overvalued for Greece, the ECB is no lender of last resort to them and they cannot handle their debts without a bankruptcy or strong debt devaluation (-1/2 is probably not enough; they would be on the safe side with -2/3).


They' have a between the devil and the deep blue sea. No answer is going to be nice.