Fox has already shown Rick Santorum and Newt Gingrich the door, because they were thought to be serious about running for the nomination. As for Palin, the article states:
... [Ailes ...] had little choice but to force the hands of the candidates on his payroll. In late February, Shine [Bill Shine, the network's programming chief] made calls to Palin and her husband, Todd, to ask if she was going to run for president. The Palins told him they hadn’t decided. “I’m not sure Sarah has made up her mind one way or the other,” a Palin adviser told me. The network is working hard to get a definitive answer out of her. ...About two weeks earlier, Huckabee had been called into a meeting with Shine and Dianne Brandy, the network's general counsel, to be quizzed about his intentions, and, apparently, the network concluded that Huckabee wasn't seriously considering a run. They kept him, and, recently, Huckabee publicly said that he wouldn't run.
If Palin were running, she would have had to have left Fox News. If she does intend to run and is stringing the network along until she announces, then she may pay a price in terms of campaign coverage. Palin's may be an unusual case, however. Ailes is said to think, "Palin is an idiot," according to a Republican close to Ailes.
The article also describes how Ailes became disillusioned with Palin.