"what to when Cessna stalls and right wing falls with nose of aircraft pointing down"

Ailerons neutral. Correct with opposite rudder first, then yoke forward to break the stall. Increase power and gently recover to level flight.

Next question, instructor? 😉

(I could have included closing the throttle right after ailerons neutral, but that kind of stall usually happens on approach when you're already at low power, so there's no point making it more complicated than it needs to be.)