Cameron said it is going to be the next PM who wins the election in October (a election where only 1.2% of the U.K. population are allowed to vote, by the way). And I believe that's the time when Article 50 will be triggered, though contingencies may still happen.
Anyway, the divorce is inevitable I'm afraid. EU is now urging UK to move out, and many will not be happy if the result of the referendum is not respected. The best case scenario is that UK manages to stall for a few more months, signs a free trade deal with EU, China and US as soon as possible and denies Boris in the general election... But the chances are pretty slim. We need a wise, competent politician to settle things down so badly right now, unfortunately it seems to be out of supply.