According to Bloomberg, Marchionne said that Ferrari will only stay if there is "a set of circumstances, the results of which are beneficial for the maintenance of the brand in the marketplace and for strengthening the unique position of Ferrari." Ferrari occupies a special and unique place in the sport. It's the only team to have competed in the sport since it officially became Formula 1 back in 1950. The team even has certain veto powers not granted to any other team. No other team has more wins or more championships. It could be argued that F1 needs Ferrari more than Ferrari needs F1.
If this all sounds familiar, that's because it is. It seems that every time the rules get changed, Ferrari throws up its hands and threatens to walk if things don't go its way. It may sound like whining, but Ferrari has a point. Part of what makes F1 special and different from sports like IndyCar and NASCAR is that each team builds its own cars from the ground up. Ferrari actually agrees with the cost-cutting measures but is opposed to any changes that take away from "powertrain uniqueness." Basically, Ferrari want each engine and hybrid unit to be unique.
In the end, Ferrari is more likely than not to stay in F1. The team's bosses will use their weight to sway things in a direction that benefits them because they believe what's good for Ferrari is good for the sport.