I seem to recall reading in a TNG magazine (maybe even the failed "Star Trek: The Magazine") that she was let go because they didn't have the bduget and Gene and/or the studio wanted to focus on Worf. And Gene regretted it.
Being a background character at the time, I imagine his salary went up as soon as he became a regular cast member.
You're mistaken. She chose to leave, because she was unhappy w/ the lack of direction for her character, and she thought she could launch a film career. Roddenberry was upset that she was leaving, so had her character killed to avoid any possibility of her coming back.