Is the TSB implying that the crew may have been able to escape if they had been better protected?
Interesting question.
In 1989, Tom House died in a Seahawk mishap off of Point Loma California (RIP, Tom). Tail Rotor loss of thrust led to an immediate ditch scenario. Henry Harris, Pilot Flying and the AW (Darnit, name not on tip of tongue) egressed successfully. Navy crew, all three were wearing helmets, etc, and usual flight/flotation gear.
Tom, PNF, was knocked out, as best as they could reconstruct afterwards, at water impact. Wearing helmet, when the seat stroked (they didn't hit the water gently, Henry's back was a mess for some time after the crash) his head snapped down and forehead met cyclic stick. Bad luck of geometry. Hard to egress when you are not conscious.
Even with a helmet, there is no guarantee that with a hard landing in a ditch/crash one will avoid injury ... but it's the way to bet.
Not sure how that would have helped in this mishap.