I was so certain that Snape wouldn't die in this book that I missed entirely what you saw in Chapter 2,

And, of course, you were right about that! I really didn't see how Snape's death could make sense in this book, but, cripes, I was prepared to have JKR show me why it could, and that scared me, no question.

I fear that Snape won't be satisfied until he's died for that deed. Wibble.