Life-threatening, unoccupied rollaway vehicle with personal injury. Possible and/or suspected issues: "Not-P" switch circuit malfunction; "false park"; lack of cross-module redundancy; lack of BCM and PCM redundancy; Diagnostic Blind Spot; lack of Occupancy-Brake interlock; systematic safety failure culminating in unintended, driverless, runaway Zombie vehicle with personal injury. Background Info: * Low mileage, mainly in-town errands driving. * Not previously reported quirks, possible latent defects: liftgate opening that was hit-or-miss requiring multiple unlock trunk-unlock doors + get out of the car manual attempts; intermittent off-shutdown double-tap issue to power off car; ill-timed "rear seat alert". * Reported "engine won't start" resulting in three key FOB battery replacements and a locked key FOB. Day of Incident: * Auto-lock and the EBS were not used. * Driver intent was to park and unload, then permanently park. Car was in-park twice before ultimately placed in reverse and backed into position, facing downhill on a slight slope and along a left-side stone retaining wall. * Driver thought vehicle was fully in Park. * Attempted open liftgate via "open trunk, open door" routine, which did not work, so I exited the vehicle to try the manual liftgate button, which also did not work. * Three back-and-forth "unlock trunk/doors + manually press liftgate button" did not work. * Note: Upon opening the door or anytime after, I did NOT hear an audible warning t