Perhaps, I don't understand the radar in that area, did the plane beep beep beep then gone, or where they in not in radar territory or.... I fear I don't understand the basics at this point well enough to have a valid opinion except that a catastrophic event seems likely. However, again, if it wasn't like beep beep gone, then is it possible it was dropped to a low alt and hijacked, hence leaving no debris, but of course IF, and I'm totally in the dark, but if a plane of that size is virtually always on some form of tracking system, then I would think any descent would be recorded somewhere.....
It's a mystery for sure. Bomb doesn't make sense, malfunction doesn't make sense, and hijack doesn't make sense. What else is there? Majick, hand of FSM,...?????
Very strange indeed. Very possible that civilian radar wouldn't have had contact in the middle of the SCS. Probable that some kind of military radar would have had the coverage, but doubtful that a 777 would have drew much attention until the story got out. So then the question is did any military radar have the coverage, did they notice anything, and more importantly, do they have a recording of that coverage area. People have alluded to the transponder being turned off, which would definitely complicate the radar picture. Transponders send back altitude and other positioning data that makes it easier for radar stations to track. If it was turned off, that is significant and the question becomes why.
Apart from radar, you have voice reports. In areas where radar coverage is thin or non-existent, often there are points along a flight path that are 'mandatory voice report' points. Meaning that the pilots are required to mark their position via voice report on whatever radio is appropriate at the time (different radios have different ranges). The news mentioned that they made some kind of voice report, but unclear if that was a mandatory voice report, handing the airplane off from one controller to another, standard communications, or otherwise. If they were switching controllers, I suppose it is possible that they were unable to reach the next controller, or any controller, and decided to maneuver to attempt to reconnect with the previous controller. That would be a little over the top and an extreme reaction to a relatively trivial ordeal...IOW, it wouldn't make any sense.
If they had some kind of emergency, and were unable to contact anyone, the most likely scenario is that they would have maneuvered the jet to go to the closest suitable airfield. Now, a 777 can't just land anywhere. It would have to land at a runway with the appropriate runway length, appropriate landing surface, and preferably one with the proper facilities to host it. Landing it somewhere remote without the word getting out somehow is extraordinarily improbable. That would have required the plane to avoid being picked up on radar all the way to their new destination. It also would have required an entire municipal or larger airport to be totally complicit in it's disappearance. Unlikely. Now, if it had crashed into the ocean, whether direct impact or inflight disintegration, it would have left some floating debris, oil slicks, probably some kind of oil fire on the surface...something. This isn't the middle of the Pacific or Atlantic, this is one of the most heavily utilized shipping lanes in the world. I have a hard time believing that someone somewhere wouldn't have noticed it either as it happened or within a few days after it happened.
I think the most likely scenario is that they had some kind of depressurization at altitude, descended below radar coverage (and also radio coverage), knowing that they would be in a precarious position at lower altitude approaching HK and China, they probably turned west because that was the closest land and figured they could put the jet down somewhere around there. They must not have had their navigation systems working properly because they would have been able to use GPS to get them where they needed to go, so I'm guessing they were going at it visually only. From there, who knows. Either got lost, ran out of gas, and attempted to ditch, or had a compound emergency situation that drove them into a crash or other situation, maybe they got disorientated and flew into the ocean or land. Of course, the plane could have been blown up by terrorists at altitude, but again, I think that would have left some kind of sign and also think the terrorists would have either communicated their intentions on the radio or the pilots would have gotten the word out because terrorists generally want the world to know what they did.
It doesn't help that we're dealing with emerging market countries that don't really have a history of very well organized and operated airlines and aviation doctrine. They're showing their ass now.