The most likely scenario is the the comms mast on the underside of the fuselage separated from the plane. This seems to be a known weakness due to improper use of adhesives and there is supposedly an AD for this issued by the FAA. With no comms and small hole in the fuselage, the cabin gradually decompresses and incapacitates the crew. They turn back and program the autopilot to descend, then go to sleep. The plane goes down to 3,000 feet, levels off, and flies into the Indian Ocean until the fuel is exhausted.
Occam's' Razor says the simplest explanation is usually the right one.
Reading through all of these threads today, I must say your comment makes the most sense. Tho not necessarily the Indian Ocean part.
My intuitive hit initially was something went wrong with the structure…which made no particular sense until I read your post here.
But what about the cell phones? How quickly would passengers go unconscious?