[Formendacil]

Not sure if what follows speaks exactly to what you're talking about, stryfe but it's what came up in my mind as a result of what you're saying...

Despite the deeply sad nature of this bittersweet quality, this finality is one of my favourite things about The Lord of the Rings: there is no open-ended hook for a sequel. Tolkien even attempted one, "The New Shadow" published in HoME XII, but although it is a fascinating read for a Middle-earth fan, he felt that it was somewhat pointless to explore bad guys and challenges that must pale against the enormity of Sauron and the Ring. One might say that, for Tolkien, there was simply no way to effectively "serialize" The Lord of the Rings--no way to make it the start of a series, that is: it is a self-contained story and when it's over it has ended.

The really fascinating thing about this, though, is the realisation within the book that it is only one story in the march of history. Examples of this include Gandalf and Bilbo's conversation at the end of The Hobbit about Bilbo's smallness in a much wider perspective, Gandalf's comment that the need to defeat Sauron is only one of an endless battle against waves of evil, and Sam's realisation that the light in the Vial of Galadriel ties them right into the story of Beren and Lúthien.

Perhaps that is it, though... while Middle-earth is more than wide enough to tell many, many stories, Tolkien was doing just that: telling many stories, not a single story over a series. When The Lord of the Rings ends, there is no going back for the "Further Adventures of Frodo" or "Sauron Strikes Back" or anything of that nature.