I don't need to prove anything and there isn't enough factual data to prove anything at all in any case, including how long this aircraft stayed airborne, in which direction it went after last contact and how far into an event it was without the crew being aware, if at all.
Just because the acars and transponder went offline does not necessarily mean the crew must have known, although I'm tipping it wouldn't have been much later when all hell broke loose. I don't see any reason at all why this aircraft could not possibly be within observation range.
You can run with the turnaround theory and pinging satellites, but do we really know that, its equally plausible.