Ok José... now we know this: after the aircraft turned, it descended to 12000 feet. I looked at the ground tracks available on Internet and it appears, after it turned, it was heading towards what happens to be the closest airport from the aircraft position. This airport is near the city of Kota Bharu where the Boeing could land. In case of an emergency where the aircraft would still fly, this is what I would do. I am convinced now that this was an inflight emergency.
The only thing that would allow the aircraft to fly for a while would be crew incapacitation but even if this is the case, at 12000 I dont think it would end up south-west of Australia. I could be wrong but I think the aircraft crashed much closer (or ditched, this would explain why they would still receive the ACARS pings as the aircraft (or parts of it) floated.
Some witnesses (fisherman) saw low flying aircraft that night... unless they are clowns, I would definitely send some boats that can re ceive the pings where they believe the aircraft went.
Yves