Geek question for someone who hasn't read the entire trilogy: what were the Sheliak, Tzenkethi, Miradorn, Jarada, Tamarians, or Dominion doing during the Borg invasion?
The Dominion would've been totally unaffected, since the Gamma Quadrant wasn't invaded. As for the others you mention, I know the Tzenkethi are mentioned in the trilogy and subsequent works, but I don't recall references to any of the other specific civilizations you mention. But a number of other, more prominent civilizations do play a role in Destiny
and some of what follows.