I have some experience lecturing on FBW flight controls, and instructing in a simulator. Aircrew tend to follow A drill, rather than do nothing. The usual reasons for following the wrong drill are rushing into action based on only one or two bits of information (probably the audio warning and the speed readout failure in this case), reverting to type (flying the aircraft/action they are most familiar with, e.g. TOGA loss of IAS), and forgetting the nasty little corners of the aircrew manual (no stall warner below 60kts in this case).
All three reasons for doing the wrong thing are present here.
I've also been hit by lightning IMC in the dark at 30-odd k and lost instrumentation/aircraft systems/AP. It's very disorientating, as would all the loud noises be to them. Add the bumps and you have no physical sense of what the aircraft is doing. Very easy not to recognise the stall in this situation. PNF should be cross-checking and isn't.
Power, Attitude, Trim.
The PF is flying for 15 degrees NU, power is variable as he's not sure of speed. There's no trimming, probably because he's forgotten it.
In fact, I think he's going for at least 12 degrees Nose-Up attitude right from the start of the problem.
Question please, doesn't everybody memorise the Power/Attitude combinations for t/o, climbout, cruise, descent and approach any more?
This situation should have been met with.
Take control
Set 2.5 degrees nose-up attitude and 90% power.
Cancel warnings, identify loss of IAS readouts.
Get PNF to confirm diagnosis.
Run through drills.
Recall Captain to flight deck.
What it's met with is:
Take control
Fly unreliable IAS drill calling for 12/15 degrees nose-up attitude
Push power up when stall warner sounds (instinctive)
No correct communication with PNF
I do think the Captain's failure to formally divide the tasks before leaving the cockpit is important to the last point.