However what if there's the tail problem on reducing through 80kts
Would that be on approach to base? As you also said:
En-route back to base, one minute out, slow(ing) to below 80 kts in order to raise downlink and/or arm flotation gear?
In which case you would probably be at (and likely to keep?) a low power/low torque setting. Unlikely to increase power to any great extent until the bottom of the approach? (I would guess one minute out would be about one mile, and therefore about 3-400'?)
Ergo, very little torque demanded? Very little tail rotor authority required, a bit like your 40kts example.
The only way I can see tail rotor failure requiring immediate autorotation into a city centre is if the failure happened in OGI hover? Is that fair, and do we think it
was hovering immediately prior to the accident? (That's not what they are reported to have told ATC?)
All idle speculation of course.