Recoverable ?
My own A330 simulator trials of recovery after the stab trim was full nose up and the stall fully developed was that a prolonged nose down input did help—but only initially. However, as the angle of attack reduced and the speed increased, apparently the full nose up stab was more than the elevator could overcome and the airplane pitched up regardless of the nose-down stick position.
It's not clear if the autopitch trim was operational with questionable airspeed inputs, but despite high bank angles in an attempt to keep the nose low, recovery was not achieved until I reduced the stab trim manually. Once trim was reduced manually, pitch control resumed and recovery was possible.
I cover this in more detail in my book "Understanding Air France 447", including what would have been necessary to recover from each point in the scenario. Essentially, the less skilled they were getting in to the stall, the smarter they had to be to get out of it. As we all know, had Bonin simply attempted to maintain a normal 2.5–3° cruise pitch attitude for 40 seconds (the total pitot tube incapacitation time), they would have survived just like the other crews that encountered the same phenomenon and made it OK.
The appalling thing is that the stall warning was going on for over 50 consecutive seconds (plus significant aerodynamic buffet), and the only thing done to recover from it was to apply TOGA power (which at that altitude gives very little additional power over normal cruise setting and zero additional power over climb thrust). I attribute this to training stall recoveries only at low altitude with an emphasis on "minimal altitude loss." This amounts to applying TOGA thrust and reducing the pitch only slightly—what AF447's crew did. But when the airplane was falling at 10–20 thousand feet per minute about the only thing Bonin could think of was pulling back to make the airplane stop descending. For that is where his training of sticking a low-time pilot in the seat and tell him to just follow the flight director did all 228 a great injustice.