My position is that RC should not make assumptions about what is in a competitor’s mind. Logic says no one would take a penalty and not refinish. The RC does not have the authority to penalise a boat for hitting a mark. It’s an overreach to apply NSC if the RC assumes a boat has touched a mark and therefore decides the boat has broken a rule and therefore the manoeuvre is a penalty turn and therefore the boat has not finished and therefore is NSC. Record finishes and protest if you feel you want to be involved. There’s already enough of what we Australians call bush lawyers in our sport. Let’s not encourage any more. 

A lot of chat for a rather simple case.

To me... there are 2 halves to OPs question...

1st half - was Red racing?  Yes.  Her stern was still on the finish line when she broke rule 10.

2nd half - Did Red tack and gybe in accordance with 44.2...namely 'promptly' after the incident? This question is subject to the protest system, just like any other allegation of a breach of a rule not exonerated.

So the RC registers her second crossing i.a.w. Finish (a), and if anyone (RC or another boat) is unhappy about it, they can protest her for not exonerating 'promptly'.  Otherwise her 2nd crossing finish stands.

-------------------------
As for the r23.1 discussion, Racing is a time-block from time-a to time-b.  Once you pass time-b it's over.  You can't restart.  If Red had met the interpretation of Case 127, then she was past time-b.  Not racing.

If a boat not racing breaks a rule, then apply RRS 60.5(c)

If a boat has broken a rule when not racing, her penalty shall apply to the race sailed nearest in time to the incident.

What am I missing?

Yes you can only postpone before the start. You can do it in the last second. 
You start when the flag is removed so, if this had a few seconds delay, the start would be late but there is the posability of postponment. 

Just follow the procedure and be practical. 

But, unless I am misreading the original post, the “restricted finish” in this case is 2/3 of the way up the course and nowhere near the starting area. The only boats playing in that area are the 18s and the H16s would only be there when finishing. So, again, I’ll ask, what issue are we trying to resolve by restricting this finish?

Agree.  As long as it's getting our of RRoS ok.