[oiuygtfrtghyju]

Bankruptcy can happen for a country.

Happy exporting something to Somalia and getting a Somali currency bank check as payment - No?

It's trickier to go bankrupt if your country use somebody else's money. Would you sell to Greece and accept euros you can spend in Germany - Yes ?

[mfukar]

True; expulsion (or leave) from a monetary union will also effect the euro considerably, and those issues (mistrust, bond revaluation, etc.) can quickly evolve in an avalanche effect. No sane person in the EU wants that.

[oiuygtfrtghyju]

Also physically a bit tricky. You would have to announce it in advance, to allow time for the new currency to be produced - in which time everybody would hoard euros. Then everyone waits for the new currency to fall like a stone, so nobody uses it, so no tax revenue.