The fiscal cliff has no leeway on what gets cut - its 10% off everything. Why should the USMC take the hit?
You're right that it's 10% off everything, but there's some debate as to how restricted that will be i.e. the 10% might be applied to each individual programme within the weapons procurement budget or it might be applied to just the weapons procurement budget...in which case, the F35 is the elephant in the room.
But the likelihood is that sequestration will be replaced with more responsible cuts...perhaps as high as the $500 billion currently on the table (but definitely looking to be at least another $150 billion at the low end), in which case the whole programme is completely fvcked, and the USAF end up with an order in the hundreds rather than the thousands.
Either way, I think the B is quite possibly already a zombie aircraft, in a world of $trillion deficits, will congress see a necessity for a hovering, supersonic, stealth aircraft with all the bells and whistles, just to act as a close air support aircraft for the marines...IMHO, no.