That's not a guarantee. What is virtually a guarantee is that if both Rick and Newt stay in the race and split the vote in states with winner-take-all by district rules, mainly Pennsylvania, West Virginia, Illinois, Wisconsin, Texas and California, then Romney will collect enough delegates from those states to put him over 1,144. Unless they come up with some magic trick to make sure Romney never gets over 30% of the vote in any district in any of those states.
There are no guarantees.