If they could win, then maybe Cameron gets the boot from the Conservative leadership. But what would happen if there was a hung parliament? Could that happen? From a quick glance at Wikipedia, that honeymoon period lasted about three months for Brown, so the premise must be a GE before September. At that point, could Labour have got away with 38-40 % of the vote tally? I think that is reasonable.
So, two plausible scenarios: Brown wins the election outright, the conservatives have to seriously question their leaders as well as tactics, maybe they turn away from Cameron‘s liberal conservatism into something more radical, or maybe they move even closer to the Centre, perhaps like the German CDU. Then again, Labour is almost guaranteed to lose the next election, so the conservative leader could be the next PM.
The other scenario, I guess would be for Brown to win, but for labour to not get enough seats for a majority: a hung parliament. At that stage, Cameron may cling on, and we might have a Labour/Liberal Democrat coalition government or some sort of deal. I think that such an agreement is going to end up pretty badly for both labour as well as the Liberal Dempcrats, considering the collapse about to occur.