Kerry has enough delegates (yes?).
So what happens if God forbid, he dies?
What happens if, after he is chosen as the nominee, he dies?
I’m sure each party has a contingency plan around somewhere. Remember, this is just party politics…there are no laws on the books saying what must be done. If Kerry kicked the bucket at any time prior to his official nomination, my guess is that the party would look to #2, ie Edwards, to carry the banner. If the nominee died after being nominated, but before the election, then it would be up to the party to decide who to field as a candidate. They would probably try to draft Hillary.
The really interesting question is what happens if the winner of the election, not the incumbent, dies before the Electoral College casts its ballots. They could concievably vote for anybody. Setting up the nightmare scenario…Kerry gets elected, is offed by Bill’s drinking buddies, and the Democratic electors vote Hillary into office without her having to run at all! :eek:
Yeah. I know. My tinfoil is too tight. 
If he dies before the nomination, the party will choose a new nominee at their convention. If he has already chosen a running mate, they might choose him.
If he dies after the nomination, depending on when he dies (how close to the election) and state ballot laws, the party may change their nominee to the VP nominee (or anyone else, for that matter) and inform the states of the change. If it’s too late to change the nominee, then the dead guy’s electors will have to choose who to vote for in the electoral college.
If he is elected, and dies before taking office, then the VP-elect becomes president immediately upon innauguration, as per the 25th Amendment.
Oh my.
If that happened, the John Birchers would take their weapons and head for D.C!