My condolences to the pilot.
I went to the safety course last year - good luck and it's well worth it.
*If* the investigation rules out mechanical failure or maintenance issues, and *if* it is true that the mast and blades ended up separated from the main wreckage, then mast bumping would appear to leave a tell-tale set of marks on the bump stops and the rotor mast breaks in a relatively identifiable place. The rotor mast and blades would usually fall a distance from the fuselage. I used to check my 22/44 for marks on the bump stops before each flight, I think a lot of people do, it's not something one wants to see.
Carb icing (or any other loss of engine performance) leading to rrpm loss, followed by failure to successfully enter autorotation and catastrophic rotor stall often chops the tail in a relatively identifiable point (I think it's the third sheet back from the tail rotor, plus the blades would cone up, but from recall of accident reports, I don't remember seeing reports where this caused the entire set of both blades to separate - Richard Mornington Sandford would probably be the UK expert on this stuff, and what the indicators are which they use to determine cause.
The reports often seem open-ended, because a precise understanding of the start of the sequence of events simply cannot be established. And without investigative expertise and access to far more information than we have, only the experts will figure it out.
It is a source of unease to me that most Robinson pilots have the low-g mast bumping issue rammed into us repeatedly, but it still appears to happen (whether in this incident or not) more than I'd like to see. I find it hard to believe that all the incidents where it happens can be attributed to poor pilot skills, but clearly events still play out in a way whereby reasonable pilots still end up in a fatality.
This may only ever be cleared up when very lightweight and inexpensive data recorders become available for these small rotorcraft,
Lafite.