I always felt that they missed their chance to not have additional DS9 characters be aboard the Defiant in First Contact, aside from just Worf.
The problem with having additional DS9 characters aboard Defiant in FC is that that leaves you with three options:
1) Kill them, which wasn't going to happen.
2) Bin them (coma?) for the rest of the movie, which feels like a cheap way of removing them from the rest of the movie.
3) Keep them around, which alters the dynamics of the rest of the film and makes it less a TNG film and more of a crossover film. For instance, if Captain Sisko is present, he can call-out Picard's craziness with some level of authority, versus his TNG friends just bowing their heads and refusing to stand up to their captain.