As I remember the immediate procedure for an overspeed was Pitch.
Pitch up and reduce the prop speed. Push the Feather button to reduce prop speed.
Pulling the cut off also shuts off the fuel so that would shut down the engine.
As to what would seize and stop the engine...well roll the dice and take your chances. I know of at least on case where the complete prop and gearbox departed the aircraft after oil starvation.
Every DC-3 I flew...feathering was accomplished by a feather pump on an Electric motor. Pushing the feather button started the pump. When appropriate pressure (450- 600 psi is memory serves) is reached a valve shift occurred via the prop governor in the prop hub.
It was an extremely simple system and not prone to too many errors.
That being said I did lose a friend in upstate New York when the engine failed to feather on a ferry flight (Engine failure not an Overspeed).
Some of the reasons the system failed to feather the prop:
Pressure switch would cut off the pump at too low a pressure....(it was possible to get around this by holding the feather button in)
Weak Electric motors. Screwed up electric motors were known to pop breakers and overheat before reaching proper pressure.
Additional the oil line (Aeroquip, Flexible) running to the prop governor from the feather pump lead a hard life and was subject to deterioration rapidly. I've seen many a line rupture. I believe that was the cause of the New York crash...but the aircraft was destroyed by post crash fire.
Three things I never flew a DC-3 without:
Fire Detection
Fire Suppression
Feathering.