As far as I can tell, Donald Trump's grieving process works more or less completely in the reverse order from what you would expect from a rational human being. Immediately after the event, Trump was more or less in acceptance mode, saying he was proud of finishing second, he loved the people of Iowa, he was going to come back and buy a farm there.
Then he went into depression, secluding himself for an uncharacteristically long time from twitter and the media.
Working backwards, he skipped over bargaining and went straight to anger, blaming the media and their unfair treatment of him.
Then this morning, he went into denial mode, basically saying that the Iowa loss never even happened and there should be a do over.
But if you look deeper into Trump's twitter rant this morning, and you have some understanding of both his neuroses and the cynical way he plays his followers, you can see that Trump has already decided how he will react to a loss in the GOP primaries, if he suffers one: he will refuse to accept the results and run third party.
Look at what Trump is doing here. He is complaining about a series of events that are, by any objective measure, ordinary politics, and he is treating them as evidence of "fraud" or that the results of Iowa were somehow completely illegitimate.
Based on the fraud committed by Senator Ted Cruz during the Iowa Caucus, either a new election should take place or Cruz results nullified.
— Donald J. Trump (@realDonaldTrump) February 3, 2016
As Trump always does, he is clearly pre-complaining about anything even potentially damaging to him as the result of "unfair" treatment or a fixed, "unfair" process. If he should lose New Hampshire, he will do it again, even though the RNC booted National Review from the upcoming debate in order to mollify him (and yet allowed an openly anti-Cruz moderator onto the stage).
Trump is prepping his followers to bolt with him for a third party run if he loses the nomination. In fact, if he loses New Hampshire and South Carolina, he may just do it pre-emptively. I suspect this is a decision he has already made. Now, I know that he will probably not be able to get on the ballot at this late date in many states, but the point will not be to win, it will be to damage the Republican nominee, which has been Trump's goal from the beginning of this process.
Personally, I think a three way race between Cruz/Rubio, Trump, and Hillary will end up pretty well for the GOP. There's a lot of evidence that a majority of Trump's support comes from disaffected Democrats, and there are plenty of Democrats who are less than enthused about voting for Hillary.
I just wish that if Trump were not man enough to accept the will of the electorate, that he would go ahead and declare that he's running third party and save us all a lot of trouble.