I had noticed that, so DHs have no idea where the boundaries sit?
They probably have a better idea than they did before.
Under the old scheme you had to consider deaths per thousand of the population at risk per year. Which you averaged over a five year period. This works fine for any large industry with many thousands of people involved. However for your typical military aircraft the population at risk is normally in the low hundreds, if you're lucky. This meant any accident that caused death of a first party made the airframe intolerable for the next five years as you'd have to multiply the small population and the fatalities by whatever factor was required to reach 1000.
At the same time a logical reading of the 3rd party tolerability boundary, 1 death per million of the population at risk per year, meant you could happily kill 60 civilians a year and remain tolerable.
So as guidance it was notably unhelpful. Ultimately I'd suggest DHs consider any deaths intolerable in the current climate and are working to remove the risk as well as they can with the levers available to them.
The TAS would have alerted the pilot of the doomed Puma as to the location of the other craft, and improved his situation awareness.
I'd agree with that but I don't know that that would definitely have prevented the accident if the crew had been heads in looking at the TAS they may not have seen the balloon at all.
I note that you talk about TAS, what happened to the original fit of TCAS, as installed in the Bond Super Puma?
I don't know that TCAS was ever considered. For aircraft that spend a lot of time at low level it doesn't really give you anything extra as the RAs are suppressed below a certain height.
Whether they would have been effective or not with a banking helicopter we will never know.
They would not have worked in this situation as at no time did the cable cross part of the airframe where they would have been located, ie the nose. The rotor took the cable to the tailboom avoiding the fuselage completely. What I found interesting is that other helicopters have hit balloon tethers with the rotor disc and not suffered any notable damage.