Proof of what?
Variations in course are a normal thing for these tracking sites. The aircraft was en route to Beijing and its course...until near the last, was in accordance with that.
On the night it happened, I heard one report that the transponders from the aircraft itself showed an abrupt departure from course, slowing of speed, and abrupt drop in altitude of several hundred feet in the few seconds before the transponder went dead altogether.
IMHO, this is indicative of a catastrophic failure and disintegration of the aircraft at speed and at high altitude (35,000 ft).
If that indeed occurred...we are still not sure at all why it occurred. My own opinion is that it is more likely a human induced cause, and perhaps terrorism.
But until they find the flight and voice recorders, and can see some of the debris, we will not know enough to be sure.
I am not a 777 pilot, but it appears the 777 has primary and backup generators on both engines, a generator of the APU and a RAT.
“.....disintegration of the aircraft at speed and at high altitude (35,000 ft).”...
Should have left one hell of a large debris path, no matter where it went down. The key word is “Disintergration”.