I honestly don't know.
The only way I see Henderson winning is by decision.
The only way I see Diaz winning is by a finish.
I can't see Diaz finishing Henderson, but I can't see Henderson grinding down Diaz for 25 minutes either.
He'll try the Condit gameplan, try and keep it in the center of the cage he's a big guy for Lightweight and has good kicks and cardio so he can keep resetting for five rounds.
I don't think he's mentally strong enough to stick to it though, the Edgar rematch showed that he can get too emotionally involved. I believe when Nate goes to telling him he's a bitch and he ain't shit that's when he'll fly off the handle and begin to get boxed up and/or choked out.