Well, there has been input, (by
Owain Glyndwr) that recovery may have been possible at various altitudes. Owain indicates that a reasonable "unloading" of the wing/reduction in AoA could be done with a steadily-held 10deg ND and in fact lower down, (thicker air), the recovery would be slightly quicker.
Aerodynamically I could well imagine that recovery was possible until quite late in the sequence. Maybe even down to 10 kFt. After all it is a conventional tail airliner and they were not in a spin. So the Tail was in free airflow. With full ND elevator and maybe neutral or at least less extreme NU trim it is liekely that the Nose would have dropped sufficiently to at some point re- attach the airflow over the wing. Might have taken 30s sustained ND or even more but personally I don't share the pesssimism that it wasn't technically possible.
It is more the practical probability which I would consider exteremely low. At no time the crew appeared in a mental constitution to unambiguously diagnose what was going on and to act accordingly and sustain that action until it yields the results (which could have taken rather long and decided action, much much longer and decidedly than they seemed to be willing to pursue a scheme). It appeared they tried something and if it didn't yield within seconds they reverted the action.