He got over confident in his GnP when he fought Werdum. Don't expect that to ever happen in a possible rematch.
I believe he'd take every round decisively and win a unanimous decision (at worst). At best, he knocks Fabricio out.
Why?
Because Fedor is still the greatest fighter in the world. Don't believe that? Then refresh your memory by taking a look at this:
http://www.youtube.com/watch?v=77QoN2P90b0