As Dr Alf and others know, David Cameron has already said that he will not serve another Parliamentary term after this one.
In reality, he will have to step down sooner to allow for an orderly transition, even if the Conservatives look like winning the 2020 election.
In reality, he is mentally in his next big role, so in this one, he is marking time, whilst his chosen successor George Osborne moves into the role.
The Referendum is a done deal and if the British public vote the wrong way they will be ignored.
Some concessions will be made to assuage public opinion but nothing substantive will be done to reduce immigration or cut EU budget contributions.
David Cameron may not look much like a winner but then neither do some of those that might succeed him and the Labour and Liberal Democrat parties are unelectable jokes as things stand.