I'm not sure of the legality of a Kerry withdrawl. I do think the damage would be too great for his replacement to stand a chance.
Remember in 1972 when Tom Eagleton withdrew as the dem's VP nominee, the Democratic National Committee met and selected Sargeant Shriver as their replacement candidate. It's provided for in the party rules. Perfectly legal.
The media will take no small hit on this if we prevail either. It has been TOO long coming, but the fact that they have covered this up for so long will be obvious to a few more converts. They got too bold, and finally got enough rope to hang themselves. It won't be a coup, but another blow the the mainstream "media" cabal.
While it would be disastrous for the party for this election, it is only one election. In four years comes another election.