At these descent rates, a very high airspeed is required, consistent with possible flutter and loss of the flaperon at some altitude before the main impact.
It doesn't.
EDIT 1:
The quoted descent rates do not require a very high airspeed. In the AF447 accident similar rates of descent were achieved and maintained throughout the descent at very low airspeeds. The quoted descent rates are entirely compatible with a recovery from a low airspeed condition.
Besides, according to Inmarsat engineers in the Journal of Navigation "it is prudent to discount the measurements between 18:25:34 and 18:28:15 inclusive, and the one at 00:19:37."
EDIT 2:
ALSM wrote: "With no pilot intervention, there is no AP or AT control after the second engine flames out, even after the APU starts. " Since my reply has mysteriously disappeared, I repeat that ALSM's observation confirms the system operation as I described it earlier.