I don't think Jordan's problem is planning. I think that he has gotten used to getting huge paychecks for his novels and is loathe to give up the money just to finish a story. (The same thing happened to Raymond Feist) Unfortunately, he is losing too many readers. In 1990, when his first book was released, it was a new sub genre for fantasy. Since then there have been the likes of George R. R. Martin (who, unlike Jordan, can actually kill a character or two) and a slew of other writers who can produce similar products.

Rowling doesn't have the same issues when it comes to her books. She probably makes more off the licensing of her characters than she does on the books themselves. And despite only having one book to go, she has four movies to go. Four movies, four releases of toys, four new licensing opportunities. All of this leads to an ability to remain true to the story.