It's tough to say. I say that because we're all very aware of what Royce is capable of, but there's a lot of mystique around Bruce. Just looking at this thread, apparently Lee trained in a bazillion different martial arts and was a master of them all - Not really, but I'm sure you get my point.
From what I've seen, Bruce practiced a brutal, non-sport style of kickboxing (call it Kung Fu, Wing Chun, Jeet Kune Do, whatever). One of the key aspects to his style in this fight is the importance he placed on distance. Royce has never had explosive takedowns, and Bruce would be sure to keep him at the end of his striking range. It really depends on if Bruce hit hard enough to keep Royce from muscling him to the ground.
The second the fight hits the ground, Gracie wins. If Royce gets stuffed on the takedowns or never can get in range to grab him, Lee by KO.