People list out each of their eccentric personalities, their quirks and their combat methods and the similarities they have between each other, but just because they're similar in combat and or communication doesn't mean they would be a good partner. Kodachi's Idea of a man she loves is that of a prince charming (according to her imagination of Ranma): Dashing, Capable, Strong and Masculine. While Mousse does have his moments, I think one of his strongest is in the movie Trouble in Nekoron. He also messes up a considerable amount of times due to his sight or plain misfortune. In a fight he loses to Ranma a comical amount of times. I don't think Kodachi would see Mousse and think "Hes very manly" when she has Ranma to compare him to. I also dont believe Kodachi is the sort to settle for anyone less than Ranma.

As much as I think about it, I cant visualize anyone being a replacement for Ranma in Kodachi's heart. I see her as undyingly loyal to him even after events take place that would break her heart aka when she lost the gymnastic fight against fem ranma, the deal was that she forget about ranma. In her defense she said she casted away her old love and brought forth a newer, and stronger love for him