Re: Of course the original referendum is only "advisory" it is not legally backed.
There's a pretty good chance Brexit will not happen (as David Allen Green has pointed out). It is significant that Cameron didn't invoke Article 50 immediately which (short of unilaterally abrogating treaties) is about the only way that the country can leave. To invoke Article 50 there would have to be a PM elected who was willing to do it, and whilst it might be possible to do it by executive action under the Royal Prerogative (which would probably require a cabinet decision), but I suspect that any PM will really want a Parliamentary vote behind them. It's always possible that might not happen - the considerable majority of MPs are in the Remain camp.
It might be that even Boris might not press the button given the noises he's making. Of course all hell would break loose from the exit camp (or at least the convinced wing of the exit camp) if that happened, but stranger things have followed. Then there is the thought of a bit of horsetrading. .
I'd put the odds of article 50 not being invoke as high as one in four, albeit the probable outcome is that it will be and there will be a deal where a lot less changes than people might expect.