P.S. If true, the "unidentified object" tracked by MAF comes back in play. The plane was in the air for the total of 5 hours. That makes 3.5 after it was lost by the military radar off Phuket. Continuing on the same heading at a reasonable cruising speed, it would've ended up in Maldives or Lakshadweep.
If someone shut the transponder off and headed out, they had to know that crossing Malaysia they'd be picked up on radar and probably visually spotted as well. The logical thing to do would be to make another turn once off primary radio and out of sight of land - so don't assume the same heading.