It's a mystery still but all the peripheral evidence suggests either an abortive hijack attempt which explains the plane's disappearance from radar and subsequent communication via the craft's transponder to receivers on the ground, suggesting continued flight west. I rather think the pilots resisted and the plane dived into the ocean.
The only other reasons could be total collapse of all communication systems resulting in the pilots attempting to get home steering 'blind' without any electronic aids....again the plane falling into the ocean.
And finally a successful hijack - all communication systems blocked by computer experts and the plane taken to a secret destination, where it remains still.
Yet what would be the point of a hijack - hijackers look for publicity for their cause and we've heard nothing.
I'm afraid it looks as if this plane is under the waves or has crashed on land somewhere. I really hope I'm wrong.