Because the PC's arn't minions, they go over their Strain threshold and become unconscious. Minions are a practical way of showing a Narrative aspect such as Han Solo shooting at 30 or so Storm troopers on the Death Star and not being immediately wiped from existance.
PC's are the heros if they don't survive your story then you have no game!
Also, who determines whether or not an NPC would die? Only you as the GM can decide that. If it's an Important NPC then you keep them around. if not they sacrifice themselves. Do whats good for the story and fun of teh game, not the rules. Hold your group UP not BACK.
Edited by jimjams79