Why the collapse of the euro is equivalent to the collapse of the EU

In the comments of many important European politicians slip the idea that preserving the integrity of the euro and the European Union is, in general, the same thing. But some, commenting on recent developments cast doubt on this point. They note that the single market existed before the advent of the euro. They dream of how Germany and a handful of other countries form the "Eastern Euro", and France led a group of "western euro", and all this will not affect the integrity of the single market. They are wrong. In fact, such an alignment would mean the collapse of the euro area (by which I mean a situation where France, Germany and Italy will no longer be part of a single union with other countries, that is out in Greece from the euro area by this definition does not fall), which, respectively, lead to the collapse of the EU. The collapse of the EU will cost the continent more expensive than the collapse of the euro area. It is extremely imprudent to assume that the single market will survive only on the grounds that it existed before the advent of the euro (although, of course, any time he can still hold).