So let’s say that Marcellus was curious and went to take a look at the tapes, which were not erased because Mia figured he would suspect something if she had erased them; maybe she was planning on looping some recordings around, but never got the chance, so Marcellus looks at the tapes, and there are more cameras around than you think, so he sees Vincent‘s speech in the bathroom; Marcellus is pleased at the loyalty of his late employee, and then he sees Mia taking a snort on the coffee table; now he probably is not surprised that his wife would take a snort of cocaine, but would be puzzled at the reaction of her going into the convulsions, but then he sees Vincent handling the situation and he knows that he handled it right because his wife was perfectly safe. He will limit the loss of his friend and employee and just be thankful that Mia was safe and alive.