Then they don't leave the EU. And at least 52% of the British electorate would be after their heads.
I won’t believe the Brexit will happen until they actually go through with article 50. The drive to world government is too strong so I will not be surprised to see Parliament drag its feet in not triggering it.
There is already a push for a second referendum that will have to be debated in Parliament because there are two million that have signed on to the petition for such.
http://www.bbc.com/news/uk-politics-eu-referendum-36629324