If Conor is smart and comes in with a solid game plan, he should have too much skill for Diaz. Good boxing, nasty kicks, real power, a chin, etc. He needs to stick and move. Don't try and KO Diaz. Control the distance and outpoint Nate.
The question is whether his gas tank will allow him to do that for 25 mins against a cardio machine. It'll be tough. He should spend a large chunk of the fight jamming Nate's leg, slowing him down and limiting his mobility. That may help Conor weather any Diaz attacks late in the fight as his gas tank empties.
He also needs to solve the question of how to land his uppercut. Nate was there for the uppercut repeatedly, and Conor saw it, but couldn't get the distance right. Nate was a southpaw whereas RDA is an orthodox fighter. So Conor needs a plan to exploit Nate's vulnerabilities and land his full range of big power shots. Maybe throw some head kicks. But, above all, be patient, conserve energy and move around. Win the exchanges and pick up points.
Can Conor depart from his pressuring style and play a more patient, stick-and-move type game? We'll see. If he can, he'll probably win. If he can't, he'll probably lose.