Plane Flew For 4 Hours
SaturnV
Based on the Wall St. Journal reporter's accounts, the pinging lasted for four hours, at 30 minute intervals. So there was power and a functioning communication link during that interval. Depending on whether the U.S. can triangulate the location of each ping, that would give an approximate a location at the time of the last ping. That leaves up to a 30 minute flying distance from the point of the last ping.
According to the Journal reporter's radio interview, he mentioned several times that U.S. officials haven't ruled out the plane landing, or crash-landing on land.
This is beginning to look like either a sudden depressurization related pilot incapacitation or pilot initiated deliberate destructive action.