If anyone is up for an unusual challenge, the sim is attached.
Switch the 4x FET's for diodes, switch the 2x NMOS fets for any you want. I've turned the PWM down as far as I can without ripple affecting the FET drive but it still takes a while to sim. Once it's done look at sysBad, once that goes positive look at the Fet-drive power and also the current going through D4 or the FET's, which should have stopped once the floating component dissipated. There's some odd RC network keeping them on!