well you could say that, but she's making billions of dollars everyday off the sales! Why end a good thing?
Take R. A. Salvatore, how much do you want to bet that he'd never in a million years think that Drizzt would be that popular? I bet he thought it was a one shot deal until after his first trilogy, then when the bucks started flowing in, he decided to continue.
My prediction is that Rowling will continue, will make up another bad guy, or have Voldemort stay alive, or have one book per Horocrux, or something to that nature! Either way Harry WILL marry Ginny, and Ron WILL marry Hermione! Why? Because I said so!
Evil confetti goddess! *bows*