The episode is designed to make Worf look romantic, ready to sacrifice for love, and not another Starfleet robot who eschews personal commitment for the mission. Maybe it would have been better to show it earlier in the season, but it contributed to DS9' s attention to relationships....
Now, the circumstances of said death, I think we all agree were pretty bad. Placing Change of Heart near the end of the season and letting her die there would have been much better.
...
The only problem I have with that is what it does to Worf's character. Could the audience really forgive him for leaving Jadzia to die? I suppose they could still have him come back for her and have her die at the end of the episode, but then he's still at fault for not turning back soon enough.
The problem is that there were supposed to be consequences for worf and that we never saw any.