It is not altogether clear that Congress would follow its (stupid) 1872 precedent that electoral votes cast for a dead person (in that case, Horace Greeley) would not be counted, and thus that the dead person would not be considered by the House.
And if you read the law proposed by Professor Kalt (it is very short, and included at the end of the third linked posting that I listed in this thread’s post #2), Congress would not be able to determine who the substitute candidate would be. If Hillary died, her runningmate would be the candidate that the House would be able to consider, and if her runningmate was dead as well, then the Hillary electors would vote again to replace Hillary with someone else. I guess that, in theory, both Hillary and her runningmate could die and the Democrat electors (all of whom will be liberal Democrat hacks) cunningly could replace Hillary with a RINO that could win 26 state delegations in the House), but by far the likeliest result would be that they would replace Hillary with John Kerry or Elizabeth Warren or some other liberal Democrat.
And if dead people can’t be considered by the House, and Trump is the one that dies, then the House would have to decide between Hillary and Sanders. Wouldn’t you rather have the House be able to vote for Trump’s runningmate, or a replacement that the Trump presidential electors selected?
That does address most of my concerns, though I hate to imagine who Clinton or Sanders will pick as a running mate (it will almost certainly be a young, far left-wing Hispanic, preferably gay).
I do still think that the election going to the House and one of the top three candidates dropping dead is a pretty unlikely (although not impossible) scenario.