As I pondered up thread, I think, at the very least, he's going to try to change the optics that he left of his own choice.
Yesterday's statement was all about blaming others and not himself. The official photograph that were released inside no 10 could have been photos of him coming in number 10 celebrating election victory. Coupled with the reference to how some of the public will be sad. Can't remember Brown, Blair, May, Major, Cameron or even Thatcher saying that.
What you might have expected, considering the circumstances, was him driving off with a teary look, covered in shame.
So my guess he can hope he leaves in autumn looking like the wonderful pm he is on his own head, smiling and waving "yes I was marvellous, but I really must leave now"