In comments at The Captain’s Quarters, “Judge Crater” writes:

There seems to be no amount of time that is too small (at least in New Jersey) to invoke the “Torricelli Option”.
With the RNC so late, Bush had problems as it was in Illinois. I can’t imagine trying to pull the “Torricelli Option” off in 50 states.

To effectively replace a presidential candidate, you don’t have to exercise the “Torricelli Option”; all that has to happen is the Democratic electors have to agree to support a single candidate when the Electoral College meets in December. A few electors might run foul of “faithless elector” laws if they supported someone other than Kerry, but (to my knowledge) nobody has ever been seriously punished for violating them—and, besides, the deed will have been done, as there’s no way to revoke the vote of a faithless elector.

Besides which, the odds of this happening are about zero; even if Kerry melts down due to blowback from Rathergate (a prospect that’s dubious at best, unless it turns out some higher-up in the campaign typed the memos himself), it’s hard to believe any Democrat consensus candidate could emerge other than Edwards, who’s already on record as lending credence to the memos.