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.
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