Gingrich will have to get at least what Santorum could have pulled. Even pulling 50% of the remainder will allow Romney to more than clinch the crucial first ballot, where most of the delegates must vote as assigned. We can hope for the miracle.
From what I understand, Santorum is going to endorse romney, and the polls on the subject always said, if Santorum dropped out, half and half split of his votes between Mitt and Newt. But the one unknown is, how angry his supporters will be because of him endorsing Romney, that has never been polled.
One half of Santorum's polling is 12-15%, and that would at least give Newt a big bump..