Just finished it. Man, that was intense. Each of the past three books has been increasingly grim, increasingly thrilling...it's remarkable (and exhausting) how well she keeps raising the stakes.
The scene with the Inferi was pretty terrifying. That's gonna give kids nightmares...not to mention the eventual cinematic translation.
I do think she'll wrap it up with one more, but it might be closer to 900 pages or so...
And whether or not Hogwarts opens next year, I'm sure the characters will return to it, and the final showdown will probably be there as well.