Whilst some here are harping on about helmets, I not aware that the actual cause of death has been made public. An it's none of our business really.
It's possible that a helmet, or lack thereof, had no bearing on the final tragic result?
As an aside, a particular pilot in PNG took to wearing his helmet whilst flying the Twin Otter, much to the shock/horror of the passengers. Sad to say his helmet failed to save him during a subsequent accident.
Horses for Courses!