Why it come down to Mitt and Newt? If anything, based on delegate count and states won, it would come down to Rick and Mitt. I’m pretty sure Rick will tell delegates to vote for him.
On the first floor vote Rick’s delegates will vote for him. When any candidate fails to get the 1144 votes needed to be the nominee, his delegates will be free to vote for somebody else. They look to their failed candidate to tell them who he supports. They also listen to floor speeches, other prominent party leaders, etc. but when Rick comes up short, and he COULD throw his delegates to Newt, he won’t. He’ll suddenly become a Mitt fan just like he was in 2008.