“but it is always possible that it landed without exploding- in a sparsely populated area; not in the ocean.”
A landing requires roughly 8,000 feet of runway. Plus there are likely five or more radios on board, not to mention cell phones if they’re in range of a tower. It’s very unlikely to have landed unless it was hijacked to, say, North Korea. If that were the case, probably the various intelligence agencies monitoring NK would know already as NK is probably under continuous surveillance by one or more countries.
Undoubtedly, most western nations have turned on their satellite cameras as they passed the area in an effort to garner clues. The automatic picture review would spot something that size if it were not there yesterday and flag it. No, most likely, it went down in the water. It could have gone down in dense jungle and also completely disappear, provided it did not burn.
I am going with the pilot going to the can and the 27 year old co-pilot turning the plane nose down and plunging it into the ocean.
Have they determined if the oil slick is fuel dumped from the Malaysia Jet? That would indicate the pilots knew they were in trouble & planning a hard landing (or a skilled Sully) - but to not report a problem is very strange. Too many abnormal circumstances to be considered a ‘routine’ accident.