If both pilots became disabled, and unable to respond to calls from the cabin crew, would the cabin crew have any means to open the inviolate cockpit door?
Yes but only if both pilots are incapacitated. Pilots can reject any attempt to open the cockpit door through procedural means from outside.
IOW The cabin crew can try all day to open the door from the outside, but a conscious pilot in the flightdeck can prevent this each and every time.