How long does it take to turn an aircraft?
How immediate would the diversion be?
Is it feasible for the pilots to say Goodnight to Malaysian airspace, all ok at this point, then notice the smoke and decide to divert, reprogramme the flight to turn to the nearest safest airport. Would the plane have the range to make that turn before entering Vietnamese space/ making an unsheduled and unnoticed maneovre in Vietnamese airspace.
And at what point in he above were the comms switched off? Before the pilots said Goodnight Malaysia?
Sorry if I am being a dafty