Dual power supply switching circuit
You are misunderstanding how depletion mode MOSFETs work.

Here's the I_d vs V_gs curve for your FET:



Notice that when Vgs is 0, the device is not shut off. It shuts off when the gate voltage is substantially below the source.

In fact I would not call this "normally open" operation, I'd call it normally closed.

I think what you want is an enhancement-mode p-channel MOSFET. Then the channel will conduct (instead of shutting off) when the gate is pulled below the channel voltage.