It was not that the inhabitants rejected the future--
Allegory. I wasn't talking about the inhabitants, I was talking about the message of the story.
Kirk says they came as soon as they knew, well, something, and Spock says they came because they thought there was nobody there. This would very nicely fit the idea that Kirk came as soon as he became aware that the PD was moot - while Spock laments that this was a mistake because Mr Atoz is still very much there.
Well, it's a theory, but it also opens up other problems. Does Starfleet (on behalf of the Federation) have discreet spy-sats in the Sarpeidon system, or are we to believe that Starfleet suddenly has sensors that work over interstellar distances that we've never seen before? (Some episodes speak of "long range sensors," but they never struck me as effective over many lightyears. If they were, why would Starfleet need ships?)
Even then, Starfleet would have known about the decreasing population. It would takes years—even assuming no new births at all—to move the entire population of a planet, especially if there was only one Library. So whether the sensors are local (spy-sats) or interstellar, the Federation would have known something was going on long before the last few hours.
The bit about Zor Kahn the Tyrant suggests the Sarpeidons have had the time portal for a good portion of their history—that it was not built for the sole purpose of escaping the nova. And that puts a whole new spin on things. I got the impression Zarabeth did not come from the same era as Atoz because a tyrant who scatters political enemies to the distant past would not bother rescuing the peons. He would save only himself and his circle of elites—setting themselves up elsewhere in history and damn the paradoxiquences—while the "little people" left behind would roast with the nova.
(On top of everything else, Spock said he recognized Zor Kahn from the archives, yet Atoz said there was very little on recent history. So again, we can have a story with non sequiturs, or no story at all.)