This stagnation have nothing to do with the Euro. It would have happend anyway maybe it would have been worse. The common market makes it easier to trade between countries and saves company time and money. Where do you think the US would have been with 50 states with boarders and passport compare to the common market. My guess is that living standard would not have been at the same level
Socialism is bankrupting the countries of Western Europe. Now that the Constitution has been rejected, individual countries may start their printing presses again (France, Germany and others already have incurred deficits over the allowed level). This will drop the Euro's value compared to the dollar.