Hi, Jeff.
The enable pin on the D24V50F5 can be connected to voltages as high as the voltage of the source connected to VIN. When EN is driven low, the regulator’s output will be shut off (and drop to 0V). The exact amount of time it takes for the output voltage to fall will depend on your load, but in most cases it will be fairly immediate and would not give a Raspberry Pi enough time to shutdown.
I am not sure if this would work for your setup, but another forum member posted their circuit for doing a delayed shutdown for an Arduino, which you might find useful. That circuit uses our pushbutton power switch, so it requires a button to be pushed to turn on the power and then pushed again to start the power off sequence.
-Claire