Looks like Chekov actually Captained a couple of different ships in the novels. He is mentioned as the CO of the USS Cydonia in Shatner's The Return
and he is also noted as having been the CO of the USS Undauntless.
Of all the books I think The Sundered
nailed his character post TWOK. He was depicted as a somewhat damaged individual that begrudgingly took the job of XO for Sulu. He performs his role in a much more guarded and cautious manner due to his experiences aboard the Reliant. He eventually fills the role comfortably and performs superbly as I remember. He does go on to eventually take over as the Starfleet C-in-C in the Shatnerverse.
As for Uhura, her comments in TSFS pretty much sum up her ambition to me. "Peace and quiet appeals to me Ensign." Uhura always struck me as the one member of the crew that was versatile enough to leave Starfleet and still be happy. I could see her pursuing music or teaching. She didn't seem to need Starfleet like the rest of the main crew.