After his third place finish in Iowa, I don't see how he could stop the Cruz vs. Rubio dynamic from occurring. He dropped out because the polls showed that Rubio caught up with him in New Hampshire, his bluster about "unfair rules" and whatnot was just BS, he knew he was going to lose either way.
If Trump narrowly beat Rubio in Iowa for second place and managed to win New Hampshire, I still don't think much would change. Rubio's strong second place would still probably lead to Kasich, Bush, and Christie to drop out, and then the Establishment support would coalesce around him like OTL. Trump would split the vote with Cruz in South Carolina I guess and turn Rubio's narrow defeat into a victory there.