You know for about a week before Hallows came out, I was a bit worried that would happen. But I knew that Mrs. Rowling would never do that to us, and she didn't. If she had, I probably would have been very empty inside. Angry and bitter, but mostly empty. I would say "Wow" and that would be the end.
Except for the riots, of course...
In a way it would be rather cool, though. She dragged us along for about ten years with this amazing story. We were blown away. Then in one paragraph, she undoes the whole thing... almost like magic.
I'm really glad that it wasn't a totally happy ending (like a certain other bestselling novel which was recently released that may or may not include vampires and a freaky mutant baby) because that would be just as bad. You don't build up for seven books for a "happily ever after," do you? No, you can't have a ton of conflict and a clean break. As terrible as this sounds, I'm glad some characters kicked the bucket.
If I ever have several big bestselling book series, I think I'll end one with the "all just a dream" ending just to tick people off. The it was was so cliche, that now it's become so rarely used that it's not cliche anymore, so I could pull it off.