The return of Sauron

Just a curious idea that struck me. Does anybody think there could be a sequel to the LOTR with the return of Sauron? Could he yet be resurrected, like Gandalf was? As Gandalf said, the shadow always takes shape again after a defeat, paving the way for an unlikely yet possible comback for either Melkor or Sauron perhaps?

The reason I bring this up is because I cannot see how ME would just go on being ruled in peace (after the fall of mordor) forever. Old nemesises either return, or new ones emerge. So how would ME be subject to a serious threat again?