Quote from
Idle Thrust:
"...has it been established that with the THS at the end of its range (13), with full nose down SS, the elevator would not have enough effect to lower the nose?
There have many posts about using the trim wheels but has it been confirmed that the only way to lower the nose would be to move the THS?"
Don't think anyone can give a reliable answer to that. The problem is that, by the time the THS had reached 13NU (an incidence of minus 13 deg), the aircraft AoA was very high indeed, but we don't have a figure yet. It seems to have been around +40. The THS was no longer producing negative lift as it normally does; it was producing positive lift.
In my
piece this morning, I argued that if the PF had selected full forward stick,
"...the EFCS would have selected full down-elevator, and started trimming the THS in the nose-down-trim direction."
The minute taken for the THS to return (if by auto-trim) to 3NU would have involved a very big height loss. Normally, the THS retrim would increase pitch authority. What I did not add, however, were some tough questions.
Was the THS already stalled (aerodynamically)?
If so, was it beyond its CLmax?
Would down elevator have therefore reduced THS lift, causing aircraft pitch-up?
If pitch-down by down-elevator didn't work, the movement of the THS towards a more neutral setting would increase its own AoA, deepening its stall.
Too many unknowns...
PS: mm43, guess you just beat me to it? 
PPS [EDIT]: Just a reminder that mm43's super graphic uses an aircraft AoA of over +60, which represents the situation at the end of the flight.
Footnote [EDIT]
Having slept on this one, now realise that I foolishly omitted the other important nose-down input that was available to the crew at the time we are discussing: thrust reduction from TOGA to idle. This they did...