Dehner didn't ask for what happened to her either, but her character was different than Mitchell's. That coda tells us a good deal more about Kirk than about Mitchell, IMAO.
The plot reason for Mitchell fading momentarily, of course, was to establish that he still had limits and could be made vulnerable (it also ratchets up the tension - in principle, this kind of near-miss drives the audience crazy, like when the search party just misses McCoy hiding behind a rock in "The City On The Edge Of Forever"). Arguably, demonstrating Kirk's compassion is the other reason for it - although that's a cliche so well-worn that the writer doesn't really earn points. No TV hero of the day would shoot a defenseless man. No-brainer.
And I've been misspelling Sam Peeples
' name as "Peebles" again - d'oh! I've gone back and corrected that where I've noticed.
Shoot a defenseless man? Pine's Kirk did and it almost got him and his newly minted ship sucked into a black hole. Just sayin'.
And I mentioned Dehner and
her last minute change of heart. Even then, she had been seduced: "You can't know what it feels like to be a god," or words to that effect.
Anyway, you do make a valid point about how the "Jim?" moment serves the plot. I just think that it does a little more than that.