Its an interesting question. The Kaaya vs Rosier debate is similar to the JW vs Perry debate. One is the much better passer, the other is the better athlete who can improvise when a play falls apart.
This isnt a knock on Kaaya, but Rosier's ability to run with the ball stressed defenses a lot. When Kaaya declared I wasn't that disappointed. I thought having a QB who could run for 50-60 yards a game would be a back breaker for defenses. Sure enough, Miami didn't lose until the last regular game of the season.* I don't think we go undefeated the whole season with Kaaya but Njoku would have been a difference maker.
*Btw I blame 95% of the Pitt loss on Richt himself. I read the day before the game that Richt was throwing the team a huge Thanksgiving celebration on Thursday night. I knew we were screwed. It was a cold noon game against a physical Pitt team that had nothing else to play for. We were the bowl game. Miami was looking ahead to Clemson and the players were unfocused after a night of playing grabass. Richt should have had the team starving, mean, and angry.