I wouldn't be so sure that Merkel is "pretty keen" for us to stay. If we "demand" that certain things change which Europe as a whole sees as unchangeable, they are not going to give.
It isn't only about money and economics. A united Europe is far stronger in the eyes of other international players. We would become automatically less "relevant" to the USA idf we were not part of Europe.
It's not a question of childishness. Nobody is going to negotiate a treaty under these circumstances unless it is to some extent in their interests, whether it be GB, the EU or Outer Mongolia.
Voted in but renegotiate.
And I can't help thinking we need them more than they need us and that we are deluded if we think they would fall over backwards to keep us in or offer us the world if we were to leave.