If this is true, the target may have been India, perhaps Mumbai. The ROP hates India as much as the US. They turned off the transponder and then headed west toward the Indian Ocean in the direction of their target. For whatever reason they never made it, perhaps an uprising by passengers or screw-up by terrorist pilots. They should look for a debris field in the ocean short of Sri Lanka or India.
A target in India might explain the disappearance this way: the terrorist pilots were trying to fly as low as possible to avoid detection by the Indian air force, but weren’t skilled enough to pull it off without crashing into the waves.
Or if they were at low altitude the plane would have been burning more fuel. Maybe they didn’t figure on that.