Albertz
It has been a long time since I flew the 737 & my memory is getting a little blurred with time but as I recall the fire switch does not disconnect the Generator drive just de-energises the gen through the GCU. As for the Hydraulics it is not possible to physically disconnect the eng driven Hydraulic pump - the fire swich electrically de-activates it. (You would still have the Electric pump in any case). All of the above will be restored by returning the fire switch to normal position.
Of course what you can't do is suck the fire extinguisher agent back into the bottle if it has been discharged
