I don't see any conceivable way, without massive loss of face. He's issued a statement that asserts he will not attend, etc. He can't withdraw that as being an intemperate remark. He's made a command decision. He has to follow through. Even if it's the wrong decision, it affects only one debate, and whatever primary vote "fallout" flows from absenting himself. I think the command decision increases his share of the ballots. But even if it costs him votes, his losses would be even higher if he reversed a command decision in the course of a few days. "Indecisive" he does not want to appear (channeling Yoda)
He has already made commitments to do a fundraiser for wounded warriors
History is replete with candidates who imploded because of one debate. He has given his opponents two hours to trash him with no response. All this BS about Fox being against him is ludicrous. His mug is a regular on every Fox show ...except Megan Kelly...and that’s because he has refused the invitation to come on and discuss it.