Well that pretty much nails it.
While on paper it still looks like Boris Johnson is in a great position to the vast majority of the public, the next Prime Minister is going to have to follow through with what they know is a terrible idea, negotiate with the EU with remarkably less leverage than the 'Leave' campaign thought they had, try to deal with Scotland wanting to leave, restless regional pressure groups in Wales, Cornwall and other parts of the country, as well as try not to have Northern Ireland fall back into a state of ongoing political violence.
So Johnson either has put his hand up to deal with all these issues until the next general election in (or sooner) 2020 and go to an election with a struggling economy (I doubt and the Union slowly falling apart (remember, Scotland's independence would topple the sitting PM almost certainly) or he can wait it out, let another Conservative Prime Minister lose in 2020, and become party leader upon the election loss and hope to win in 2025.
I doubt he thought this through very well. On the plus side UKIP's work is mostly done so they mightn't poll as well any more.