As long as they don't kill her, then they don't have to (immediately) be killed.
That is false. They have already attacked, kidnapped and hurt an innocent human being. Even if you argue that they shouldn't be killed because they haven't done enough to deserve it yet, the truth is they are Currently imprisoning and abusing an innocent person. That means that the monsters need to be Immediately stopped Before they do any more damage to the victim. She will be saved by any means necessary. The kidnappers sealed their fate the moment they attacked her. Those monsters are already dead. It doesn't matter what they do now, they can try to fight, they can try to deal, they can surrender if they want to. They will still be punished for the life they have scarred. All they can do is change how Long they will suffer before they die....