Alistair Campbell, I believe, always took the view that if a bad news story ran on for more than a few days - and certainly across a weekend - then a resignation was on the cards. The same was true if the messenger became more important to the story than the message. Ultimately, that was why he himself left government - you can't get the message across if you are the bigger story.
Time and time again, Cameron has ignored this advice, perhaps out of some loyalty to his colleagues or perhaps because he lacks the necessary inner steel to tell them that their time is up and is more scared of having big beasts lurking on the back benches waiting for a chance to savage him. If, as expected, Andrew Mitchell falls or is pushed onto his sword today, I don't think that it will do much to reverse the damage caused by his outburst at the police. The swearing was out of order, but the sentiment of privilege is the most damaging, as it retoxifies the Tory brand (although savage cuts to benefits for the hardworking poor don't help much, even if they are given a light dusting of public approval and branded as cracking down on scroungers).
Even though the news agenda has moved on in the past few days, the echo chamber that is a party conference has been filled with grumbles about Mitchell - who wasn't even able to attend a conference in the city he represents. The Mitchell saga also puts the lie to Cameron's speech about wanting to spread privilege.
The problem is that the message over the past few days has been that it is time to move on, although Mitchell still accuses the officers on the gate of lying, even if nobody actually believes him. Mitchell should have been sacked/resigned on the spot, because it has been obvious that this story would run and that it would become bigger than the message.
With his speech in mind, Cameron could have demonstrated his views on privilege in a practical manner, by leading and not following public and media opinion and dismissing Mitchell in advance of the conference. He doesn't look like a man in control, but one carried away on the tide of events. While that may be an accurate representation of his leadership, it doesn't bode well for his future. People don't have to like a leader to elect them, but they do have to respect them. Gordon Brown would probably have won a - reduced - majority in 2007 after a strong summer of events that demonstrated his leadership abilities.
Cameron and Osborne have probably done enough to hang on until 2015 in their respective roles, after this conference, but it would be wrong to say that the Tory party likes or respects them. I think it is resigned to having to put up with them for the time being, but I don't think they are secure. Neither looks like a winner and neither looks like a leader. If that is maintained, I wouldn't rule out a challenge over the next eighteen months, particularly in the face of events.