PFET to turn on/off system power
I'm not sure the P Channel MOSFET is being biased correctly.  Your other logic seems correct though.  Q4 needs the Gate negative in respect to the Source in order to conduct.  Conversely, if the Gate is held positive, or near the same potential as the Source, it will not conduct.

I'd flip the connections on the Source and Drain.  Also, a resistor should be between the V_Batt rail and the Gate.  This ensures that the device can turn off.  Then remove R12, and connect the junction of R6 and Q2 collector directly to Q4 gate.  This should ensure that you can turn Q4 on and off.