Cameron was already going to stand down at the next election, so I don't think you can say he's concerned about his career. It's the queen, the head of state, who's supposed to represent the people no matter what. Politicians are allowed to act like politicians, and that's the worst I can say about Cameron. He made his own views clear, he called a referendum as he'd promised, and he's ready to hand over power to those whose side won. I really don't see a problem with this. (Note that he hasn't actually gone yet, he's still running the country till his party choose a successor.)