I think it was just US union rules for Atlantic flights as standard with 2 captains.
Nah, not with the unions I have been a member of. Even flights requireing 4 pilots and over 12 hours need only 1 Captain and 3 F/Os.
That being said, the FAA wants the F/Os to be Captain Qualified so we do part of the check ride in the left seat.
Other Airlines or Unions may have different rules.
As for the Captain's Last Flight: have done a few of those whenever my prior rides have gone bust. Then just dust of the log bokk and start sending out resumes or CVs again and start over. Even some of the Captains who hit 60 or 65 or whatever the age limit of the day is/was, have come back as F/Es to boost their pensions and/or keep humping that girlfriend down South.
