If my memory is not playing tricks on me Ferrari has threatened to leave F1 before (although I i am not sure when and what the occasion was). It's just a way they will always get their way. Just like a spoilt baby in a candy store.
If standard engines are introduced F1 would not be place for car manufacturers anymore. Just a playing ground for "garagistes" like Enzo Ferrari called them.
IMHO this does not mean the sport would be less interesting. But things like KERS should be thrown out of the window when the sport is taken away from manufacturers.
I can not imagine there will not be a top single seater formula when the smoke clears. (and I do not call something like A1GP top).