I don't know where else to put this, so I'll post it here. I don't know how we got to this in another forum, but I figured it would be best if I posted my theory here.
It's about how I think Kirk, Pike, and Number One end up where they end up.
The Enterprise is said to be the flagship in SNW. If Una becomes Captain, she's either Captain of the Enterprise or she's Captain of a lesser-stature ship. Similar to when Riker was offered all of his commands. If Pike is still Captain, then the Enterprise isn't available.
Pike needs a new First Officer. Spock doesn't want to be First Officer. Spock doesn't want Command. TOS establishes this many times. Whenever he has command in an episode, he's out of his element, and people are always aruging with him. "The Galileo Seven", "The Gamesters of Triskelion", "The Paradise Syndrome", and "The Tholian Web". Pike requests that Kirk, already a First Officer, transfer over from the Farragut to become his First Officer.
In "Mirror, Mirror", it's said that Mirror Kirk became Captain of the ISS Enterprise by assassinating Mirror Pike. In SNW/TOS, it probably happens that Kirk is elevated to Captain when Pike transfers off.
Una goes on to serve a long career that's still talked about in LD, Kirk becomes Captain of the Enterprise, and Pike meets his fate.