Jadzia Dax (Terry Farrell) was one of the best characters on Star Trek: Deep Space Nine. She carried the memories of Trills before her, including Kurzon Dax who was Captain Sisko's best friend. She retained that closeness to Sisko until she was killed by Gul Dukat in the sixth season of the series. But it was a death that didn't have to happen.
It's already well-known that Farrell wanted to become a recurring character on the series in the seventh season instead of a main character, presumably because she'd gotten another job offer from Becker, but that hasn't been substantiated. Her request for reduced time on the show was denied, and her character was killed toward the end of season six. But more than just Farrell's desire to go part-time led to her decision to depart the series.
According to The Fifty Year Mission: The Next 25 Years [via Whatculture], Farrell was allegedly subjected to misogynistic comments by Rick Berman. She claimed that he regularly made remarks about her appearance, would not bend on any requested changes to her new contract, and, at one time, sent another producer to tell her "If you weren't here, you know you'd be working at Kmart."
Though Farrell didn't want to leave the series, Berman's unwillingness to work with her on a new contract as well as his alleged treatment of her led to Farrell's final decision. And though Nicole de Boer tried to fill her shoes when she came onboard Deep Space Nine to play Ezri Dax, the series was never the same without Farrell. And now, almost twenty-five years later,Farrell is willing to return to the franchise. Hopefully, things have gotten better behind the scenes for the women of Trek, and she wouldn't have to endure any negativity if Jadzia Dax did come back.