Terry Farrell played the Trill Jadzia Dax on Star Trek: Deep Space Nine for six seasons. When she asked for reduced screen time for the final season, her request was denied, and, instead, her character was set to be killed off. It was a moment in Star Trek history that got a heated response from fans, especially in how her death actually happened...at the hands of Gul Dukat, the Cardassian dictator, in the finale of season six. It was a death scene that had little build up and, though Worf's response made it powerful, it would have been much more so if Jadzia had been allowed to die in an earlier sixth season episode "Change of Heart."
In that episode, Jadzia and Worf are on a mission to track down a defecting Cardassian officer. Jadzia is badly injured, and Worf cannot find it within his heart to leave her. Instead, he stays with her, and the Cardassian defector is discovered and killed. According to a Deep Space Nine DVD featurette, Farrell thought it would have been better for Worf to have had to leave her to finish the mission. [via Looper]
Leaving her behind would have given Dorn much more material to use in the remaining episodes of the sixth season. Not only would he be wrestling with grief but with the guilt of not helping his wife. And it would have also shown the warrior side of him to be stronger as it always has been among the Klingons. Jadzia's death just ten episodes later comes out of nowhere, and though a shock to Worf, it doesn't have quite the emotional impact it would have had if he'd made the heartbreaking choice to complete the mission, accepting that his decision would mean the death of his wife.
To this day, Jadzia's death in the season six finale doesn't make sense, and it almost seems like a throwaway scene just meant to eliminate Farrell from the cast. It's baffling that the producers wouldn't have seen the prudence behind killing Jadzia in "Change of Heart."