Not necessarily. His contract could stipulate that if he leaves he could not be on any other network for a period of time...a year, two years...the amount of time left on is contract plus some extra time? Yeah, he could be about the $$$$, but leaving could also void his opportunity to be any kind of voice.
It would not surprise me that if he resigned, there would be some sort of non-compete agreement in place in his contract with Fox which would not allow him to be on another network. It's probably better, for now, that he continue to play out his contract, keep doing what he is doing, then move on. I also wouldn't be surprised, though, if Fox fires him, the non-compete would not take effect.
At the end of "Debt of Honor", a 747 is flown into a joint session of congress, killing most of them, including the President. Jack Ryan, who had been sworn in as VP after the other VP resigned, was not at the Capitol when the plane hit. Executive Orders takes place right after that, with Jack Ryan as president, and this book centers around the virus terrorist attack.
With some Fava beans and a nice Chianti.