Some similarities to G-AWAP
Take a look at the AAIB report for G-AWAP lost in 1983 off Norfolk coast.
The report concludes that the accident was caused by the disengagement of the main rotor head retention bolt, with consequential detachment of the rotor, due to corrosion of the engaging threads between it and the mast.
Not to say this was the case but as an inspection engineer that regularly flew in G-AWAP and took an interest in her fate, I was struck by the recent video and the eyewitness reports of G-AWAP, a loud crack and a detached rotor landing away from the main wreck.
https://assets.digital.cabinet-office.gov.uk/media/5422ed76e5274a1317000199/3-1985_G-AWAP.pdf