If you are going to entertain those thoughts are likely, well then you can just as well write a scenario where France invades Ireland because of its low company tax rates.

Will they bring wine and promise to mandate decent bread?

Up to now things would are going in a single direction: more globalization (which essentially means more control by a small cadre). The Euro is a part of that narrative (with the implicit notion that democratic control is replaced by the "specialists in Brussels and Frankfurt").

So, irrespective of the monetary value (and I would dispute that it would be less than Argentina, because it would make all the debt void - due to devaluation and obvious inability to pay - PLUS making the Euro very unstable - who would follow next?). Irrespective of the money issue, there would be a symbolic unravel of a project. That is ideologically intolerable.

Furthermore, there is no need for patrolling any borders. There are plenty of (legal) ways to destroy a country. For instance, just see what what the current fall in price in oil is doing to some exporter-only countries. It would not be difficult to devise a set of informal things to have a devastating effect.

And if you think this is paranoid, you probably have not been seeing what is happening in the so called periphery. Even it it was unintentional (and it was not: saving the banks of the centre was deemed more important than the lives of millions), the outcome was of "paranoid" impact: if somebody, 5 years ago, came to this site and suggested the disaster that is unravelling, that somebody would be labelled paranoid or crazy (extra paranoid, as almost no one was as pessimist as reality).