Well, since the voters chose Jean Carnahan, I don't see how it stunk or how it was questionable. I suppose maybe the Democrats deliberately sabotaged Carnahan's plane in order to win themselves a Senate seat...wouldn't put it past those SOBs, right?
You are very right though, that at a Presidential level, this would be a real problem. Although I am a staunch opponent of the Electoral College, I admit this is one situation in which it would be somewhat helpful. If a presidential candidate died and there was not enough time to get his name off the ballot, the Electors themselves could choose someone else when they convene to vote, if the deceased candidate won the election. The party would, hopefully, announce their choice of a replacement candidate in advance (though they wouldn't HAVE to), but the fact that the dead candidate's name was still on the ballot wouldn't be a problem other than in the confusion it would cause to voters.
If the election were decided by popular vote, this could still be remedied, but there would have to be a law stating the exact order of succession of Presidential candidates. Presumably the VP nominee would become the Presidential nominee and then would choose a new VP nominee.
Actually, I think the Republicans sabotaged Wellstone's plane because they knew they could beat Walter Mondale.
Maybe you're right and it was legitimate. I guess he died too close to the election to replace him on the ballot, and the voters knew that his wife would be appointed in his place. I have had family members in politics, so I know about political shenanigans. I think when electing somebody, the whole thing should be above-board, and as long as that was the case, it was probably legitimate.
What was not legitimate about that election is that the Gore campaign and Jesse Jackson filed suit to keep the polls in heavily Democratic St. Louis open late, after the rest of the state's polls closed, and it turns out the man in whose name the suit was made, claiming that he had been unable to vote due to long lines at the polls, was dead.