Has leaving a monetary union ever been carried out before, in an electronic banking system?
If there is any hint of a Eurozone state leaving the Euro, there would be so much capital flight the economy would be crippled for decades.
The more likely answer is that "said country" gets kicked out if it blows up (because other countries will probably follow). Or Germany/France will vleave voluntarily. The key point - will Germany/France prop all these countries up if one or two blows up (meaning others will follow)? My bet is that they will try to but eventually realize they'll be taken down if they do.