I have a theory about Book Seven. It involves spoilers so is after the break.
In each of the last three books the person dying has been more and more important to Harry Potter.
In Book Four it was just Cedric Diggory, a fellow student, whom Harry was a not very close friend of.
In Book Five it was Sirius Black, who was his newly found godfather.
In Book Six it was Albus Dumbledore, the man who had been a father figure to Harry for six years.
Now J K Rowling does not do things without a purpose and a pattern, so my theory is that the final challenge for Harry will be how to cope with the death of someone even closer.
Therefore either Ron or Hermione or maybe Ginny will die in Book Seven is my theory.