Earlier quoted context omitted.
If exit negotiations take a few years, and the European wanted to offer the Brits a face-saving way to change their minds, they could adopt some internal reforms / offer Britain a better deal. Wouldn't have to be a perfect deal, just good enough to justify having another vote.
That's the last thing they will do because then it would encourage every EU country to hold a referendum and do the same thing, which would kill the EU easily. [What I see as more likely is that the UK invokes Article 50, goes through a financial crisis, and then the EU offer to cancel our Article 50 invocation and let us stay in the EU if we join the Euro and Schengen.]
I think if one more country votes to leave between now and then a renegotiation and some core constitutional changes become more likely.
The basic problem is that the Leave side lied about the benefits of leaving, but they were absolutely correct that the core of the EU has become a neoliberal financial dictatorship with rather thin democratic wrapping.
If bigger cracks start appearing in the structure the leadership is going to have a choice between accepting more real democracy, or having the whole thing come crashing down.
Currently there are no bigger cracks visible, but the economic foundations in most of the EU are very shaky - so who knows where we'll be a couple of years from now?