It sounds good in theory, but humans only have a finite amount of energy. The risk is McCain might become exhausted from trying to forge a consensus, and consequently might appear tired and cranky in the debate.
As for the question of Friday night's debate, which some in the media seem to think more important than saving the financial system--if the negotiations are still going on in D.C., McCain should offer to send Palin to debate Obama! Or he can take a break from the meetings, fly down at the last minute himself, and turn a boring foreign policy debate, in which he and Obama would repeat well-rehearsed arguments, into a discussion about leadership and decisiveness. And if the negotiations are clearly on a path to success, then McCain can say he can now afford to leave D.C., fly down, and the debate would become a victory lap for McCain.