Old 'imperial' Europe had invested a lot of political capital and hard work in forging the idea of a united Europe and if the more than 5 decade long experiment of a European political and economic union collapses,then its conceivable that the inherent set of contradiction that led to the collapse would also seriously imperil the current warm ties between the countries.
Old Europe came together at the end of the bloody world war to form a European union towards preserving the power and influence which it had accumulated after centuries of global warfare and political deceit,in order to do it had to eschew the competitive nationalism which had wrecked Europe's inter continental empire in the first place.Old Europe traded nationalism for global economic influence,an arrangement which i think is now beginning to unravel and as a consequence Europe has already begun to side step collectivism.
The expansion of the idea of European union into the margins of Europe has only added to the doubts surrounding Europe's ability to act collectively.The influx of cheap labor into western Europe from impoverished economies in the east has seriously fractured the political consensus that existed in the western capitals,France,Germany,Italy,Spain and UK do not view this problem from the same angle and the political costs incurred by each country also varies as a result.There is also no consensus on how to resolve the problem of migration from non European countries and Europe's collective effort to integrate them into its mainstream is again a bag of mixed results.
Europe appears more and more like a divided house and what divides you can not only disunite members,but make you spar with each other.One would really hope that Europe knows better.
P.S:From the Indian perspective while we may wax eloquence how a united Europe makes the world a better place,a fractious Europe,esp western Europe,is not necessarily an unwelcome Geo-political prospect.