horizontal stabilizer is still a major part of this situation, as I mentioned in previous post. I suggest the horizontal stabilizer left the plane and that was the cause of the near vertical dive. No control. Bank from ailerons was worthless. 

The de-ice for the horizontal stabilizer is electrically heated leading edge, while the wings themselves are heated tubes supplied by bleed air from the engines. Bleed air also heats the air inlets on the engine nacelles. Perhaps the heated tail wasn't keeping up. It's hard to melt ice when it's -47C.

One problem....if you have reduced engine power,  you lose bleed air. The converse is also true....using bleed air also consumes engine power. It's also hard for me to believe there wasn't hail in that cell. Heavy ice ingestion can lead to flameout. Remember the heated surfaces and generators for the electrical power need the engines cranking full.

I'm not sure about the horizontal stalling, but a big load of ice on it could result to "tail flutter", which is a harmonic vibration due to undesigned air flow. Too much flutter and the wing (tail in this case) can cause structural failure.

We are all speculating at this point. Arm chair q-backing.