Kakashi must not have put up much of a resistance if Sasuke could pry Sakura from his arms so easily. It's odd. There's nothing to be gained from killing her besides an overly emotional responce from Naruto.
She has her seal, so if Sasuke managed to stab her she would be ok?
Not if Sasuke decapitates or mutiliates her to such a degree that her seal is incapable of regenerating the parts.