I don't think the Grand Prix is going to be cancelled. This will probably be the last tournament that Zuffa does. Plus the way Barnett and Dana looked at the Summit, I think Barnett is secure.
I actually don't think SF is over, I think Zuffa will keep it around and use it to run GP events in the future at different weights maybe as well, I think it will become like the the K-1 of Zuffa where all the credible belts will be held in the UFC, SF will still have there own champs but it will be the GP winners that hold all the credits.
AT the end of the day SF does have a strong fan base, it is still on the rise, it is making Money, its not really harming the UFC, it does have a good TV contract, why would Zuffa buy it and want to destroy it when they can use it as an extra part of there organisation running a slightly different angle like hosting the GP's and it be a win for them.
In fact SF could be good the the UFC, because if Showtime views that may have the channel to watch Boxing get into MMA as well though SF then they may start wanting more MMA and start buying UFC PPV's.
Does not really make sense for a company to buy a company that is doing well just to destroy it even if you beak competition form there existing company, when they can run both situationally with a slight twist, the GP'd been the answer, and do well with both, as for bringing fighters from on promotion to the other, they can do that anyway without closing one off.