And who would have become the operations officer on bridge?
The obvious choice would be Seven.
But that would have most likely meant that there would have not been Astrometrics onboard Voyager.
Or... perhaps there would have been. Perhaps Seven and B'Elanna had to build it together. And since Harry was B'Elanna's buddy, she would have had another reason to resent Seven, and being stuck with her in such an assigment would have not made her any happier either. Now Kes on the other hand would have tried to guide Seven through the possible difficulties of working with another individual without the ability to be as "one mind". B'Elanna, who has practically nothing in common with Kes, would have not liked her hanging around them. So it could have been an interesting storyline for an episode - three so different persons trying to find a common ground while Chakotay was in the background keeping taps how their work progressed.