I really do think if Rousey went for broke on a takedown, and landed it immediately, she'd take Floyd's arm home with her. I'm not even kidding. You have to give him zero grappling credit. If they fought an mma fight Rousey would win a few, maybe more than a few depending on the success rate of the takedown. Obviously the male boxing champ wins every time he is able to land a punch before she takes him down. It's not a matter of her striking or his grappling because they are worlds apart, it comes down to a punch versus a shot, and the shot wins sometimes.
She wouldn't be able to touch him.
I have only read the last page and don't know how this came about but it is entirely possible that rousey clinches and trips then arm bars him before he lands a ko shot. With a gi on it would be even more plausible.