What makes you think they would be able to fly it to china and hide it before anyone notices it's missing?
If it's a test or experimental aircraft there will be number of chase aircraft, numerous data recorders and it will probably be videoed the whole
time as well.
You can't just jump in a plane and fly it off without anyone noticing either, You'd need a bunch of people just to get it prepped and started.
What about the range? A b-2 could probably just make it (might need air refuelling though which would be very difficult) but an F-22 certainly wouldnt
have the range on internal fuel.
Then there is diplomatic disaster that would happen if it somehow did transpire that a top secret aircraft was stolen.
On the other hand, plenty of times in the past it has been tried.
I have posted this article before, maybe you would find it interesting
www.acig.org...
(Best to cut and paste into Word or something so it's easier to read, green text on black, what were they thinking?

)