That diode might screw things up. With ~0.7 V drop across the diode, plus the Vout-low of the 809, the voltage at the PIC might not be low enough to reset it. Maybe a Schottky diode would be better.
You could also put a voltage divider on the INPUT of the 809 with the bottom of the divider going to the C0 signal. The input current to the 809 is pretty low, so you could use fairly high resistances. This assumes VDD is not greater than the maximum allowed for C0.
But, stupid question: doesn’t the PiC have brownout detection, precluding the necessity of the 809?