Instead of taking them out, have your NPC's ask for a concession, that way they are out of the fight, but not destroyed, and can come back in later scenes, if the PC's don't take the concession, let them take the consequence and keep fighting. That way if the PC's are out for blood, they will find out how tough these bad boys are, and if they just want to accomplish their goals, they don't have to slog through all of their consequences.