If McGregor can avoid Chad's power, and stuff his inevitable takedown attempts, I think Connor's unique striking ability and leg kicks will take it's toll on Mendes. Both fighters are used to dominating their opponents either by KO/TKO or winning by unanimous decisions.
Mendes has an edge, because he has faced the best fighter in Featherweight division (Aldo) twice, and has gone a full 5 rounds with the champ.
This is Conor's opportunity to shine though, and he knows it. A loss to Mendes will pop his attention whore balloon, and be a major career blow for him. I don't believe that McGregor will let Mendes get inside and negate his length advantage with dirty boxing and clinches.
Conor will wisely keep his distance, and pick Mendes apart with strikes from all angles. I don't think McGregor will run through Mendes by any means, but I do think he will win convincingly enough to justify the hype and setup an even bigger fight with Aldo.
Lawler vs. MacDonald 2:
Robbie Lawler doesn't strike me as the type of guy who will be able to keep the belt for any length of time. Lawler won the first matchup via split decision, but I think that Rory has/will learn from that fight. Rory is more of a tactician, whereas Lawler is more of a tough as nails, brawler type.
I think this second fight being 5 rounds favors Rory. Lawler has been known to gas late in fights, and wouldn't be surprised if MacDonald uses those championship rounds to his advantage. Look for a weary Lawler to get taken down late in the fight, and for Rory to finish him off there.
My Picks:
McGregor
MacDonald