The public was told some things about Maastricht and the Euro, which it believed. Unfortunately these things have turned out to be in conflict with reality. And that puts it nicely.
That leads to certain problems. You cannot tell voters that you screwed them and then get them to agree to your newest proposal.

As for leaving the Euro we are approaching a very ugly area. The EU has quite limited means to enforce its treaties. If a member state insisted on leaving the Euro, the EU probably could make it leave the EU altogether. However, it is doubtful that the EU as a political project would survive that. The lawyers would be told to find some way and nobody would look closely at it. A bailout was also supposed to be strictly forbidden once.