Ever since Reagan cleaned Carter's clock in that final debate before the election the conventional wisdom is front runners only lose ground in debates so why risk it?
In this case, if he doesn't show up, Mitt is going to look like the Bain analyst who is crunching the numbers and playing the short odds instead of looking like a leader who gets going when the going gets tough. Which is to say his absence will make him look increasingly arrogant, impatient for the "coronation"; in short, stands to lose more than he will gain by not being in attendance.
I've worked around these Bain guys and it's not the free market capitalism that offends people. It's all the gutlessness and shrewd calculus that people are sensing. It comes across as cold, almost reptilian. This is what makes Mitt the perennial 24 percenter; the loser to the loser.
Time to go big or go home