Tail stabilizer was tampered with because of the way it was found with very little damage. It did not appear to be separated forcefully from the plane at all. I suspect it was somehow loosened prior to the flight.
When the tail falls off it disrupts the electronic controls of the plane and the pilot must accelerate speed in order to gain control. He may have done that which caused the engine to torque and break away, or the engine may have also been tampered with in some way causing it to break away when the plane was rattling.
In any case, I smell a rat.
Tail is a "Buck Rogers. Space Cadet" word.
The "tail," the aft control serfaces of aircraft and attaching stabelizers are two different items, each of two main parts. If Vertical Stableizer is lost, it takes rudder with it. This results in some loss of directional control, but A/C can be flown and controlled to safe landing by use of ailerons and asymetrical thrust in engines. Not fun but can easilly be done.) The video you see from Coast Guard of them lifting piece of A/C with "AA" on it is vertical stabelizer.
If horizontal stableizer is lost and/or attached elevators are shed, all control is lost, because of the needed effect of horiz stab in all realms of flight.
Comments about electronic controls and "accelerate speed" are complete BS. Nothing personal, but there are a hundred reasons why A/C could crash. None of them are as described in your post.
Yes AB300 is fly-by-wire. So are most commercial A/C, and all military A/C in production.