If attempting an under-the-RADAR / unseen pass thru to Pakistan:
The aircraft likely attempted a route between Bangladesh and Burma ... Bhutan ... Nepal ...
Somewhere along there, detected by Red Chinese air defense, the aircraft was probably shot down in between mountains.
There, are so many places to lose airplanes, and the allies lost many there during World War II.
If the Red Chinese could locate the “black box,” they might transport it to some spot in the Indian ocean where governments would like the aircraft to be found ... and then the Red Chinese would announce that the Red Chinese heard something ... down there southwest of Australia.
Is my guess.
I believe that if the black box is ever found, it will not contain any information that helps explain what happened to the plane.
It was a spiteful act by the pilot and co-pilot to make the plane disappear (very likely in the Indian Ocean).
The last words from the cockpit, I believe, will prove my theory.