There is also the fact that we don't know the ultimate fates of McCoy, Chekov, or Uhura. And we know nothing about Sulu past the 23rd century. Those are "TOS" stories I'd like to see. Not 5 year mission stuff I know but still.
Uhura was Chief of Starfleet Intelligence in "Catalyst Of Sorrows", set in the 2350's/60's (Lost Era novel). That story also features a young Ben Sisko.
Apparently she was still active in Intelligence through 2377 ("Vulcan's Soul" trilogy, Memory Beta).
Chekov became first officer of the Excelsior and served under Sulu into the early 2300's (Forged In Fire/The Sundered)
Chekov also became Starfleet's Commander-In-Chief at some point. (The Return/Federation)
Chekov was later involved with the events of the "Vulcan's Soul" trilogy, and apparently retired around 2380.
According to Memory Beta, Sulu apparently was mentioned as being the Excelsior's Captain upto 2320 (in "Burning Dreams"), at which time it appears that he left Starfleet to run for President of the United Federation Of Planets (which he won, not just once but three times, unlike George Takei's failed bid for LA government in the 1970's).
Then Sulu doesn't make a reappearance till the DS9 novel "Armageddon Sky" (part of he Day of Honor series), but he's travelling incognito.