If I understand your position, it is that if John Kerry becomes unavailable after some deadline (let's pick October 1), then the DEMS have no candidate for president in this election cycle, and a vote cast for Kerry is "wasted." Or, that the candidates (Kerry, Edwards) follow the same line of succession, i.e., a vote for Kerry ends up counting as a vote for Edwards. No doubt, at some point, if a candidate becomes unavailable, it is too late to change the ballots.
Electors to the Electoral College elected in each state are bound to vote for the candidate to whom they are pledged in accordance with the laws of the individual states ...
If you can cite for me, one state law that prohibits a party elector from casting a ballot for a different candidate than the one named on the voter's ballot (the one we use in November), I'll donate more $$ to the SBVfT. It's my contention that every state law permits, maybe conditionally, the elector to vote for a different person. One condition where it is reasonable for the party to instruct the elector to vote for a different candidate being that the candidate named on the voter's ballot is not available on that day in December, when the electors cast their ballot for president.
My guess is that the elector's pledge, while it might name a candidate, essentially says "I promise to cast my electoral ballot for the candidate that is chosen by the party," where the party's first choice is from the National Convention. That does not rule out later changes, provided the change is made according to party rules.
Electors are not permitted to vote for whoever some party hacks tell them to. On the other hand, there are no real penalties if the Electors violate the law. It's a matter of honor, mostly.
The number of "party defectors" is small. I think there have been fewer than 10 in the history of the country. But again, in the circumstance where a candidate is unavailable (scandal, health being two good reasons to drop out -- and those issues tend to pop up at unexpected and unscheduled times), our system of choosing a person for the office does not hamstring the political parties.
The U.S. Constitution sets forth only one requirement for serving as an elector. In Article II, Section 1, it provides that “no Senator or Representative, or Person holding an Office of Trust or Profit under the United States, shall be appointed an Elector.”
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Only a handful of states print the names of candidates for elector on the ballot. In the vast majority of states, when the voter votes for a party’s candidates for president and vice president, the voter is simply assumed to have voted for the party’s candidates for elector.
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In about half the states, electors are formally “pledged”—that is, they are legally committed to vote for the candidate of the party with which they are affiliated. In the remaining states, electors are “unpledged,” meaning that no explicit legal requirement exists to vote for the affiliated candidate. Still, even unpledged electors could face legal difficulties if they “faithlessly” voted for a candidate other than the one associated with their slate of electors. This is because the people of the state voted for that slate of electors with the reasonable expectation that those electors would loyally reflect the peoples’ choice. In fact, the problem of “faithless electors” has been more theoretical than real. About 20,000 electors voted in all presidential elections from 1789 to 2000, and fewer than a dozen voted faithlessly. The outcome of an election has never been changed by faithless electors—nevertheless, it could happen.