I'm not sure on what you mean by Diaz not having the best chin. Do you mean literally or are you saying he has a suspect chin? The Diaz brothers are tough guys and Nate Diaz has never been knocked out in his professional career or even finished by technical knock out. Just clarifying on what you mean by that.
That being said, I think he can win this fight by submission. I think his stand up is good enough to not get finished, and he has the ground game to submit Guillard in my opinion.
Psalm 30:5 "For his anger endureth but a moment; in his favour is life: weeping may endure for a night, but joy cometh in the morning."
Top 3 Favorite Fighters
1. Chuck "The Iceman" Liddell
2. Glover Teixeira
3. Demian Maia