I don't think Frank folds easily. Looks at the beating he took from Lesnar in their first fight. He held in there and got the sub. Also, looks at his second fight with him. Took a HUGE beating and didn't tap etc. As I recall it was ref stoppage. Lesnar was brutal that fight.
I don't think Roy can put anything on Mir that Mir hasn't already been through. Mir, imo, is very underrated by most.
Let me qualify what I'm about to say by saying that Frank is one of my all time favorite fighters. There have been so many fights were he was supposed to get slaughtered and he came out on top. He broke Tim Silvia's arm. For that alone he should be in the UFC Hall of Fame (calm down Earl). He also came back from that horrific motorcycle accident. And, I've had the opportunity to talk with him on two occasions. You could talk to the guy for hours about MMA. He has some many different angles/takes on all sorts of topics.
All that said, he was lucky in the 1st Lesnar fight that the ref pulled Lesnar off him. When Frank gets hurt, he folds. Even if he doesn't tap, he stops fighting and it's over. Look at the Vera fight. Or the Carwin fight. If Roy lands one of those hooks, Frank will be in trouble.
Like I said. I'm rooting for him, but this is a tough matchup.