I think they're separate issues. "Death of the author" is a principle in criticism: do we care about the author's intention in creating the text? The older version of this was the "New Criticism", which tried to read the text in a vacuum, not paying attention to the historical and biographical context of its composition. But Barthes took this further by saying that the author had no control over the interpretation, even if s/he explicitly tells us what the text means. (A related idea is "reader-response theory", which begins the criticism with the unique response of the individual reader at the time). A simplified litmus test would be if you think a writer has the right to claim that one of their characters is homosexual, when the text doesn't indicate either way.

What you're talking about is a moral judgment, not a critical one. So not saying "this book isn't good because the author was bad", but saying "regardless of the book's qualities, we shouldn't read it because the author was a bad person".