One argument in favor of many if not most of the Excalibur crew surviving is that we don't know of any mechanism by which phasers could kill the crew of a starship while leaving the ship visibly intact.
Decompression is unlikely to work against a compartmentalized starship. Phasers aren't credited with radiation effects that could "poison" the crew to death. And settings comparable to wide field stun have never been shown to be lethal, least of all against targets inside a building or a vehicle.
If the ship's phasers can be set to wide area stun as in A Piece of the Action,
why not wide area kill?