The Euro didn't fail. It has flaws (as did many European currencies that existed before the Euro), but no EU member state has abandoned it, because the upsides outweigh the downsides and the costs of leaving would be enormous. Even Greece didn't do that, although they did come close.
Europe's most successful countries are the ones with their own currencies. It's easy to compare the differences in growth and debt with those in and out of the EZ. Ireland is the only true exception & it's for reasons relating to its tax policies.
But don't over exaggerate, we are just about to see the story when one tries to play on their own without the EU. I think it's going to be the first true example of "what happens"