Cameron is weak. But one thing is for sure: he doesnt want to be the PM who does the irrational, crazy thing. And Jonson.... well Jonson was for very long time closer to Europe than Cameron. I dont think he really wants to leave EU. But he probably will have to.
Yesterday i thought Brexit is 100% sure. But today, i am not so sure anymore, i think the leavers didnt really expect to win and having to keep their promisea.