My personal suggestion regarding Jadzia's death was that the Dominion should have invaded Trill instead of Betazed, that that's what would have driven Sisko to bring the Romulans into the war, and that the season ending arc would have been Starfleet's attempts to free Trill. That would have brought the Trill into the core story of the series in a way they never were, and given Jadzia an excellent opportunity to die in battle. The ultimate direction of the series would have barely been changed at all, but Dax's role in the whole thing would have been greatly improved.
Problem is Trill is so underdeveloped (plotwise) as a planet that it would have no real significance and the only point of interest would be Jadzia's reaction to all this. But if she died in battle that would have messed up how Worf's character developed in season 7, and how Worf and Ezri interacted.
Besides by season 6 Jadzia sort of faded into the background so when they bumped her off it kind of paid dividends for the rest of the main characters, and gave the first several episodes of season 7 something meaty to portray.