I believe the hydraulics would continue to work as they do with the AS350.
No . Restarts would not drain the battery !!
I don't think it's possible that the blades stopped any higher than say 50ft , if that . There would have been nothing left , just a big crater . It must have entered an autorotation of sorts from 700ft to 50ft or so . I think it is possible the pilot may have used the brake after impact . A few seconds later the roof collapses .