If the plane didn’t land somewhere, my best guess is, the Chinese mistook it for a hostile (and remember, the transponders were shut down) and shot it down, afterward keeping everyone else out of the crash area.
Diego Garcia: Island Atoll US Base is Rumored Landing Spot for Malaysia Flight MH 370
http://www.theepochtimes.com/n3/567207-diego-garcia-island-atoll-us-base-rumored-to-be-landing-spot-for-malaysia-flight-mh-370/
Malaysia Airlines Mystery Deepens After Top Disease Experts Rushed To Indian Ocean
http://www.whatdoesitmean.com/index1754.htm
Awlrightty then, it’s been answered....