Does F1 need Ferrari? No, of course it doesn't. Would the sport be worse off without Ferrari? Yes, very much so. As has already been said, the sport is bigger than any team, however without a shadow of a doubt, if any team left, Ferrari would be the one that would have the greatest impact (and in a negative way).

It would be like Man Utd leaving the Premier League to play in the top Spanish flight. The Premier League would still survive, however should Arsenal, Chelsea, Man City, Man Utd all leave, then that would be a major blow, and not one I think it would survive. This principle applies to Formula 1, if Ferrari left, it would survive, however I don't think F1 would survive if all the top teams and drivers left to race in another series.

Bernie and co need to be careful of the threat of FOTA to set up a rival series, because Formula 1 DOES need the current teams and drivers - Formula 1 as a business would be worthless if everyone left to set up a new racing series.