I watched a documentary about Flight 447 (the Airbus flight that was lost off Brazil) and they mentioned that modern planes send tons of position and other data per flight. Seems the current system is called ACARS.
Anyway, from a probability perspective it seems highly unlikely that a plane would disappear from radar precisely at the time that a data transponder stopped sending position fixes, unless, you know, the plane crashed right there.
I mean, the media makes it sound like the search radius is "flight speed * remaining potential flight time at current fuel burn rate".
I'm pretty sure we'll find that this is the "religion of peace" again.