How about this scenario from a PM that *probably* knows he has nothing left to lose . .
PM plays the game up until the last minute, then goes to the EU and tells them we are leaving, there will be no extension asked for. PM then resigns in November when everyone starts screaming for his head.
General election returns Lib Dem with massive majority, who then try to get the UK back into the EU . . leading to another 3 years or more of bitter arguments