On B747, 757 & 767 A/C opening the door from the outside should disengage the girt bar. However if it does not all that will happen is the chute will fall on to the steps.
It requires the pack to fall a couple of feet (from memory) to withdraw the parachute pins from the attatchment before the inflation bottle is energised.
The worst that can happen is having to change the chute, if you do not have one there is a restriction to the passenger load back to base, you cannot operate from your main base with a chute inoperative.
tristar 500