I've said this before, but it's worth repeating. I don't have the exact percentages right, but its something close to this.
In the early eighties, the Canadian MOT or Accident Investigation released statistics on helicopter accidents in Canada and of all the fatalities, in around 85% of cases death was caused by head injury and of that 85%, 45% had NO OTHER injury at all. In other words many of that 45% would have walked away had they been wearing helmets.
In smaller machines, a pilots head is close on all sides to consoles, airframe, even engines and transmissions.
Obviously some of the accidents would not have been survivable and I don't remember all the details now, but the message is clear.