TC
I've just read your earlier post where you state "TRE diminishes to below acceptable on 'normal' helos as the TR speed slows even by as little as 5%, never mind even slower"
I don't think that's helpful in understanding the dynamics and capability of a tail rotor. If you're demanding max anti-torque thrust from your T/R, say high AUM, OGE Hover and spot turn, then yes, the TRE may be insufficient.
However, the T/R is perfectly capable of maintaining effectiveness at reduced RPMs if the pilot reduces the thrust demand of the T/R. In the case of an autorotative descent and landing, the T/R will be effective at massively reduced RPMs because there's not much work for it to do.
JJ