It'll be a while before they really lose FOX. FOX is dissenting just enough to try to maintain some sense of credibility. Trump is such a disaster that they're going to get laughed off the planet if they don't at least acknowledge some of it.
But if they do lose FOX, the GOP is in real trouble. That party, as much as any in history, has turned into something that runs almost entirely on propaganda. They haven't actually done anything helpful in years -- they've just filled a lot of not-terribly-bright people with cultish bullshit about Democrats being out to get them. If that brainwashing slips, they're going to be in trouble.
We can already see it with the increased popularity of the ACA. Republicans mostly hated it because it came from Obama and they hate everything about Obama... mostly for no reason other than he's on "the other team" and they've been trained to. Which is they same reason they now cheerlead Trump even when he does things ten times worse than anything Obama did. Remember all the endless complaining about Obama playing golf? Trump does it waaaaaay more, and you don't hear a peep about it. In fact, I heard some Republican voter on TV the other night claiming "Trump is the hardest-working president I've ever seen!" That, my friends, is brainwashing. And if the conservative propaganda outlets let up on it, it may start to slip some. But, it's pretty deeply ingrained at this point. It may take a generation to let that propaganda brainwashing die out.