I believe a theory is that the surviving pilot or co-pilot after taking control of the plane depressurized the cabin. Sure makes this look like a suicide of a pilot with a mass murder of all the other people.

On United 93 during 9/11, once the passengers became suspicious they immediately went to their cellphones. No one received a call from this plane. It leads me to believe the pilots were turning back to land because of some sort of emergency, smoke in the cockpit, a cargo of batteries smoking, a blown tire on takeoff burning, something along those lines. After the crew made the turn, the smoke rendered everyone unconscious similar to golfer Payne Stewart's 1999 flight. Once they turned to the new heading the plane continued on that course on autopilot until it ran out of gas.

I'm trying to visualize an honest-to-goodness miracle but I'm having some difficulty.

They might have found it.
 

Malaysia Airlines Flight 370: What Happens Now? - ABC News

I still watch ABC World News with Diane Sawyer and saw that they may have had a breakthrough. http://abcnews.go.com/WN/

The Authorities know more about this then we have the need to know.
Returning the loved ones to their families does not mean they have to be alive.

The plane crashed into the ocean and went down to the bottom. No way of "returning the loved ones to their families".

It may never be known why the plane went down except it did go down in the ocean.