Trump has a very narrow goal post compared to other candidates. If he loses, places 2nd. It'll be spun as an electoral rebuke of his candidacy and appeal, and those supporting him in N.H. S.C., and Nevada should really reconsider his viability as a general election candidate.
If Trump wins: It was expected, however Marco Rubio had a very strong showing at 2nd or 3rd, thus demonstrating that there is a demand for a more "sensible" established candidate, other establishment candidates should drop and support Rubio, and those that are undecided in the follow up states should reconsider Trumps appeal in the G.E. and support Rubio.
Trump understands Iowa's history of not picking the G.E. candidates. He's said this pretty much every stump speech in Iowa. He'd like to win (who wouldn't?), but understands the follow up states are where things heat up and true appeal is selected.
I maintain that if Trump wins, he runs the table, despite the spin of a surging estabo candidate. The Rubio camp knows this, which is why this weekend, their strategy was to push Cruz as frontrunner and not mention Trump at all, in hopes that it places in peoples minds the inevitability of a Cruz win, and with a strong showing of Rubio in 2nd or 3rd. They understand and are aware that a Trump victory is game over not just for Cruz, but all the candidates.