Inmarsat has the absolutely say over the path of Flight 370: Just dig up some existing data on how planes pin differently on the north, south, or even middle paths, they will know for absolute certainty which way 370 took.
The Malaysian government can double down to remove any doubt by flying a 777 the three routes to simulate the pinning.
In this way, they can even figure out where the plane went down.
My theory from day two: Pilot committing a perfect crime in mass murdering. The only question is did he killed himself as well, and could he bailed out from a 777?