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[Chris Scott]

bearfoil,

Having no structural design knowledge (former A320 and A310 pilot), much of your fascinating argument is going over my head. But I’m also having a syntax problem in your second paragraph. Quote:
“If the RTLU FAIL was accurate, is it assumed that it would revert to its 'protect' position, though Fail was on the screen? At .82 Mach and an unrestricted Rudder in Alternate Law II, the danger is clear.”

I may be misunderstanding your question, but, just in case you (or anyone else) is in any doubt, my understanding is that the system has to cater for a subsequent approach, go-around, and engine-failure. So RTLU failure will permit full rudder-travel. **
ECAM warns the crew that high-speed rudder protection is no longer available, roughly as follows (from memory):
RTLU 1 + 2 FAULT
USE RUDDER WITH CARE ABOVE xxx KNOTS

Chris

** (EDIT) But only after the Slats extension command has been given (cockpit "Flaps" lever selected to Config 1, or greater). Until then, the limter is frozen at the value current at the time of failure. (See HazelNuts39's post #1073 below.)