Dimande gives a start when he sees Mamoru has the heart moon rod, Usagi reaches to grab it from him, yelling “Mamoru!” They raise it up together and see in shock that “the rod is reacting to both our powers”. Dimande’s eyes widen in terror.

In the manga, it sort of does look like Dimande is going to execute a heel-face turn for a few scant seconds as realizes Wiseman is using them, and is even forced to kill his own brother Wiseman brainwashed. He even realizes he could never beat Sailor Moon’s power because it’s so strong and pure.

But actually, it ends up that he completely snaps and steals two Silver Crystals despite everyone yelling at him that bringing them together would DESTROY EVERYTHING- he doesn’t care at this point, he’s lost it. Pluto sacrifices herself to stop time and allow Usagi to yoink them away. Dimande then continues to blame Usagi for all his problems.

So Usagi and Mamoru end up just combining their powers to kill him, the true bond of love and determination triumphing over his infatuation with power.

(Dimande disentegrates, Usagi and Mamoru clutch each other and stare in shock and horror)

Nemesis: What a childish prince you were, Dimande.

In the end, Demand was not as much a person as a very specifically horrible obstacle for Usagi to overcome, a bad experience that tried to break her as a person but didn’t, and someone who could only think in terms of power. So his death is quick and almost insignificant, with even Nemesis dismissing him.

Like I said, in the manga it’s all Usagi’s narrative, and about her believing in her own power and breaking free when someone tries to strip her of it and her own self worth, using sexual domination as one of the tools. Her story is about defying that, moving on as a person and rescuing herself from that, and that’s really what the manga was about- girls believing in themselves, refusing to be held back and becoming powerful as a result.