“+4 hr @ 600 mi/hr -> 1,000s of miles.”
To stay below 18,000’ with the transponder off the airspeed would probably be under 300 mph.
If they were over 18,000 with no transponder would have set off ATC everywhere they flew and would have had intercepter jets after it.
Then it’s a conspiratorial situation where the re-directors were knowledgeable (aka Flight Crew?).
Does the Indian Ocean care about Class A airspace?
Not if they were over the Indian Ocean.