European Union is not working because too many different economies are in the eurozone. I was a fervent Pro-EU, now realising a federation of independent countries might work better than a superstate.
EU in its simplest form is harmonization of rules and a bigger market for you to sell your goods. That part works exceptionally well. I don't see a single reason where that could be a negative in a mid to long term. The euro zone, which tries to connect some very different economies is not working that great but EU countries can decide to stay out of that part.
The Euro was designed as a bulwark against currency speculators and people trying to arbitrage between imbalances in the different European economies.