I've thought about this for awhile (like, 14 years or so
) and here's what I think...
Yes, she should have died in Change of Heart. BUT, I would have made some changes to the last half of the season overall to accommodate that.
I would have placed Change of Heart at the end of the sseason, like the second to the last episode. That way Terry Farrell still gets to(basically finish out her contract and we don't lose what were some good Worf and Jadzia moments.
I would still keep The Sound of her Voice as a way to get you emotionally ramped up for what's about to happen. I'd also want to place her death after Times Orphan, I think she and Worf have a great B story there that also adds more drama to her death.
In COH, I'd change the runabout scene where Jadzia and Worf banter about their honeymoon to one where they talk about having baby. Worf's being a pessimist, reminding her of what Julian told them, Jadzia being an optimist saying that everything will work out fine (which always means something bad is about to happen).
The rest of the episode goes as it did. Worf decides to blow the mission and tries to rescue his wife but it's too late. He gets her back to the station but Julian gives him the "I managed to save the symbiont" speech.
Worf still gets reprimanded by Sisko and is told he will never get a command because of his choice but this time the tone is more remorseful. Sisko still tells him that if it had been Jennifer he would have made the same choice.
The finale can still go as it did with Dukat going to the Dark Side (that requires a whole thread by itself). Maybe he can kill a Bajoran priest instead of Jadzia. Prophets vanish, Sisko goes back home to scrub clams.
Season 7 opens not with Worf being upset about Jadzia's entrance into SToVoKor, but instead he carries the guilt of not being able to save her. The tension between he and Ezri is based on that, he is worried that she is holding him responsible for Jadzia's death. It takes some convincing from Ezri (and the destruction of a Dominion shipyard) for him to get over it.