Ferrari need exposure (and more importantly wins) from F1 so they are able to build their road cars and keep their brand high market. This is something that's been happening since the days of Enzo. They've had their runs in history in WEC but the exposure just isn't enough.
So if Liberty cancel their $100m annual bonus, they have effectively 2 options. Option 1: Quit the sport and make their own series and convince other manufacturers to join it. This will be tough and would need a mighty investment from them in just getting it going. Even then, they might not get as much exposure as they would in F1. Option 2: take the hit, get their shit together and race. Continue getting the exposure they require to build and sell their road cars and carry on.
Them leaving the sport wouldn't be good for either party.
I don't know, Porsche don't seem to need F1 to be just as famous as Ferrari.