Be they biographies, autobiographies, novels, or children's books, fiction or non-, celebrity books always see a bump in sales when that celebrity dies. And I mean immediately—I don't think some of these poor people are even cold before we start seeing reorder requests for their backlist from the major chains. This is, I think, for two reasons:
1.) News media are able to tell us about these sorts of things almost immediately these days, so there's very little delay between the death of a celebrity and the news of that death reaching the public;
2.) People become a lot more interested in something or someone once that something or someone is no longer available. Thus, once it's clear to people that a given celebrity's last book really is their last book, whether they've been meaning to read it or not, they're more likely to buy it, either for themselves or that friend they have who's totally obsessed with said celebrity.
Now, caveat: this really only works for celebrities (either people who are famous for being authors or people who are famous and happen to have written a book*). Unless you are already somewhat newsworthy, gentle readers, your demises (untimely or otherwise) will not really do anything for your book sales. Please consider this before faking your own deaths and moving to the Bahamas to sit back, relax, and watch the royalty checks roll in. (Also, turns out it's hard to collect royalties when you're, uh, dead.)
I know the chains have been reordering books by all sorts of recently deceased celebrities lately—the practice is not new—but I'm curious: are you more likely to buy a book by or about someone famous if they've recently died?
*Or, more likely, paid someone else to write their book for them.