I took that into account too and if the plane did land somehow within that 4 hour, the most logical place along that route would be Burma as the nation is still mostly closed to the outside world like North Korea and within a 4 hours flight time window. Laos or even Cambodia is a possible, but you would have to hack up allot of jungle to land a 777-200 ER.
Why hack up jungle? If this 777 is equipped for a Category 3c landing (no viz, no ceiling) then it would be easy for the Muzzies on the ground to set up the necessary equipment at the chosen landing spot and have them come on in with no lights lighting the runway dark and invisible and immediately park it in a hangar. Close the doors and no more airplane.
Did you see anything, Achmed? Nope, Mohammed. Didn’t see a thing!
What about the old airfields from the Vietnam war? How do the take off and landing requirements for a BUFF compare to the 777?