Honestly I think some of the characters were temporarily re-assigned to other ships in the fleet. Scotty was on Earth, leading the Enterprise repair/refit. As for Kirk, I have no idea. Part of that time was, no doubt, spent recovering from the experience of death, perhaps he also went to the Academy to teach. He may have also done a brief media circuit as a Starfleet hero.
Also, I'm sure that at some point the senior staff was briefed on the new Five Year Mission. Maybe other ships already on the mission have supplied Starfleet with initial impressions of what they're finding on the frontier and the Enterprise staff is taking the lessons to heart?