First, your question is using completely wrong terms. The vertical stabiliser is the fin, not the horizontal stabiliser or tailplane.
If the forward mounted screwjack should fail and break, then I expect the tailplane will lose it's forward stabilising force and would tend to go to max deflection and break. ie immediate break up of the airframe. I do not think it would remain fixed and allow you to work the elevator.
You and your friends have a funny topic on conversation in the pub!