Berto(e) wouldn't have been able to have stopped Mosley at that point (probably can't even stop him now). Berto is too clinch happy once he gets even slightly fatigued. Which would have played into the short hooks Shane likes to throw. Shane is also physically stronger than Berto(e) and would've moved and positioned Andre exactly where he wanted him, at all times. Berto(e) would get some good shots in, but would get caught in an exchange and either go into survival mode the rest of the fight, attempting to land a big equalizer. Or be KTFO with a Mosley right hand late.
I think Mosley would have won a close decision win in a war that showed his age as he gassed by the end. But a KO during an exchange was possible as well.