I do not believe any F-35 variant is going to be cancelled.
I can see the C being a very, very easy target! The navy are lukewarm and as already pointed out, if the number of air wings falls to eight then the F18C could well be phased out without replacement. Everyone's a winner, the navy have the aircraft they want, the Air Force get to keep more F35s and congress get to save lots of money. I'm more interested to see what the Air Force's opinion will be on sacrificing the number of As to sustain marine orders for Bs.
Keeping only one variant instead of cutting numbers of all 3 would, at the end of the day, deliver a bigger bang for your buck...to borrow a terrible cliche.