I don't think skipping this debate is the right decision.
During the last Nigerian Presidential election, a friend of mine who'd witnessed the event said that the opposition candidate found the debate unfair somehow and boycotted the debate. The result was that Goodluck Jonathan had the stage entirely to himself and just spoke the entire time. It was basically an hour of unrefuted, free advertising, handed to him by his opponent. By skipping the debate, it may allow the candidate to score a few feel-good points against Donald Trump, but that isn't the point now. The point is to build up as much momentum as possible leading up to the Iowa caucus, and that means fighting tooth and nail for every bit of oxygen that you can get your lungs over.
A Gingrich-Bachmann-Santorum debate could be just the ticket for the shift in dynamics that I've been predicting. With only those three on the stage, Bachmann and Santorum will have the perfect opportunity to attack Gingrich as being to their left, and show themselves up as the true conservatives. They'll each be allotted a third of the speaking time! Gingrich will occupy the left-wing position the entire debate. Without Romney, it's not worth it for Gingrich to participate.
I thought this was a spam forum post when I started reading about your friend in Nigeria.
Gingrich is already in. It'll look clumsy if he backs out now. Why would Romney mind Santorum and if they agree Bachmann and Perry ripping and cutting into Gingrich's Iowan support? Bachmann is hinting that she's leaning against this debate. I've expected her to rally in Iowa but she may not have good enough strategists to pull it off. Are she and Perry really in any position to pass on something because of the risk?