Why? Greece will just force convert all assets (and debts) from Euros to Drachmas, then devalue the drachma significantly
The problem with this conversion is Greece’s to deal with. They’ll have to do it fast, and make it illegal to hold significant amounts of Euros - and be willing to enforce it.
Truth is, there’s probably no good way to do this and avoid bloodshed in Greece - those politically connected will get to keep assets in Euros, but debts in drachmas - then will buy assets, post devaluation at significantly deflated drachma valuations - and folks will notice and string them up.
Europeans might not appreciate their debts being converted to drachmas - and do things to get their money back - things that might lead to the new German Province of Crete or something like that.....
The big and the smart money left Greece quite a while back.