Discharging MOSFET using Resistance or Diode (Best possible Alternate)
Ok lets draw your circuit properly...







simulate this circuit &ndash; Schematic created using CircuitLab

Now lets say when the switch is closed you only want 0.1mA of current to be wasted.

\$R2 = 12V/0.1mA = 120K\$

Now, from the data-sheet an IRF530 has a max gate capacitance of 800pF. So the gate will discharge exponentially with an RC time constant of 9.6uS when the switch opens. 

That seems fast enough to me...

Maybe you want 1uA... R would be 12Meg and that would put the time constant close to 1mS.