[Knight of Gondor]

I always wonder about the Great End as well. Since Tolkien based his world largly on the Christian worldview (IE Illuvatar's creation, the fall of his creation) we knew there'd have to be an End...despite the Lost Tales' suggestion that Middle-Earth became England, and that the Silmarillion's stories were like mythological tie-ins to our world's history today, being, as Tolkien thought it, devoid of enchanting mythological richness.

There is mentioned a Great End either in LT or in The Silmarillion the idea that perhaps the Elves and Men will sing in unity the completion of the Music of the Ainur. There is also mentioned a great battle (Dagor Dagorath, the final battle where Good will triumph ultimately) where Melkor (or, Morgoth) is unchained to wreck havoc for a short time again on Middle-Earth before its renewing

Whatever the great end is, it probably means the destruction of Middle-Earth as we know it, but we must also recall Theoden's and Thorin's words upon their deaths; that they go to the halls of waiting until the World's renewing.