CYA. If he doesn’t go and Brown wins, the precept ion is that he let the supermajority slip through his fingers. If he goes to MA and Brown still wins he can always blame Coakley for running a piss poor campaign. (They're already doing this, btw.)
Well, he could always pop over to Cambridge to apologize to the police about his saying they behaved “stupidly” after admitting he didn't have all the facts. Maybe have a beer or two before tying up the eastern flyway on the way back to Washington.