I don't see anything that indicates loss of main or tail rotor authority in the early part of the clip.

He approaches in a straight line, banks a short turn over the buildings, and starts a steep climb (all indicating intact authority), which to me looks like he either stalls out on, or something happens in the cockpit to restrict the pilot ability to manipulate the controls. He tries to dive out of it and/or autorotate to the ground, but doesn't have the room to get it done. No external indications (smoke, vapor trail, etc.) of a mechanical failure, but that doesn't necessarily mean they didn't lose power. Seems unlikely though as those ships have two engines.