Stick-pusher is installed to counteract the deep stall, not tailplane stall. Sadly, the fact that Q400 is not prone to tailplane stall leaked out only after the accident. There is still no official word about it from Bombardier but it's expected soon.
Primary symptom of fully blown tailplane stall is abrupt and very fast pitchdown as flaps are extended. Recovery from tailplane stall in DHC-6 is: retract flaps, cut the power, pull to recover from dive. Preferably do all three simultaneously.