The 320 has a control stick so slumping forward would not affect it. The door lock switch is on the left rear of the centre pedestal so no, could not accidentally be operated. It's also gated, needs to be lifted to operate. Incapacitation of the pilot inside would not stop the locked-out pilot gaining entry. Also incapacition would not affect the flight profile. The aircraft would continue it's flight plan. The pilot inside has selected either VS or FPA to put it in a descent.
An early solution to these occupancies would be to bring back the flight engineer.