If you study the directional microwave antenna - it acts as an 'artificial horizon / attitude indicator' ... the gyros of the camera also provide a very high quality attitude indicator - it seems to be particularly high quality - since there is very little 'horizon drift' wrt the horizon.
It appears that the tail rotor has ceased to provide thrust for a very long period of that flight - it also looks like the pilot maintains sufficient speed to prevent uncontrolled yaw rate. The degree of roll indicates the side slip - there is one 'lapse' in speed and you can see the degree of roll caused reduces as the speed reduces - there is then a short loss of control in yaw - and then the pilot regains a speed power combination which controls the yaw again - he has almost taught himself to control the machine with no yaw authority. Maybe he has never been taught this? For some reason the speed drops again - either by choice (perhaps to land in the perceived small space) - or perhaps due to to some further issue...?
Once control is lost the high yaw rate maybe causes such high precession loads on the engine bearings that the engine is severely damaged and releases oil (at least). (60 degrees per second yaw rate limit in AS350) .. or perhaps oil starvation from hight 'centrifugal' loads....
Very difficult to judge 'pitch pull' timing when yawing at very high rate...
Poor chap - very sad
- nearly makes it - is the right training given?
(refer to: Wessex in Wales and Bell 206 near Black Bush - very sad)
Vietnam era army training may not be appropriate any more?
Have you practised landings with no tail rotor thrust?
... or is it something else? - accident report.....