Ilia was last-minute, but that doesn't necessarily make her a replacement for someone else. After all, the Enterprise was rushed into service to intercept the "intruder." It wasn't supposed to be launched for days, even weeks, and that would've just been for a shakedown, not active service. So they didn't necessarily have the full crew complement already assigned and ready to go. They were scrambling to pull together enough personnel to let them launch in 12 hours. It's not unreasonable that some of the posts weren't filled until late in the game.
Agreed. And as Decker- who handpicked most of the crew himself- didn't seem to know that Ilia would be serving aboard Enterprise
, it's possible that Kirk selected her name from a list of available navigators before he left Starfleet Headquarters, knowing that someone would need to fill the position. Come to think of it, it's not entirely clear who Decker's first-officer would have been had he remained in command of the Enterprise
. Sulu would seem to be the most obvious choice, but it's possible that he had someone else in mind altogether.
Sonak was wearing commander's rank stripes on his uniform, but based on his dialogue with Kirk, it seemed as though he had only recently been posted to the Enterprise
- and given that Decker intended for him to complete his mission briefing before even boarding the ship, it's not clear how well they knew each other or if they had even spoken face-to-face.
It's not clear who the female officer was supposed to be. Various novels suggest that she was Admiral Lori Ciana, a former love interest of Kirk's who had been involved in his initial promotion to admiral and acceptance of a position at Starfleet. A photograph of the transporter accident (minus the effects) was included in a 1980 calendar, and clearly depicts a woman not
wearing an admiral's uniform.