I started Harry Potter after the fourth book came out, simply because I hadn't heard of it before. I am so glad I didn't wait for all 7, because I would have missed much enjoyment over the years by reading, rereading, and discussing plot clues with others. I am one of those who preordered and waited, in store, for the midnight releases of 5-7.
I might have been very upset if something had happened to Rowling before the final book, but she had so many notes that I'm sure we would have eventually found out what happened, even if it wasn't in her writing style. Heck, they could probably just copy all her notes, bind them and release them and it would be a hit because of all the people who will read every little tidbit of background.
