My view is that if the Uk had adopted the Euro, then Brexit would be a fantasy today. The Euro is very strong competitive currency on the ascent. But they don't have that. There is no good reason for them not to exit, after more than two decades sitting on the sideline.
My belief is the monetary union will hold together ( it has too ). But there could be new a treaty after a Brexit -- there seems to be one each decade or so -- in order to keep member states happy.
The right to tax people that have not been directly elected will not be accepted by austere people for much longer.