You would have lost system A hydraulics with no engines but still had control of the primary flight control surfaces with manual reversion in the real plane. I guess CS didn't model manual reversion in their simulation. The APU isn't approved for in flight use. And the APU will only supply electrical power to system B electric hydraulic pumps which don't power any primary flight controls except the upper rudder. The only thing system B powers is the brakes, inboard flight spoilers, upper rudder and the aft airstairs.