[Evisse the Blue]

I take it to mean: "It (the ring) is gone, and now all (the world devoid of all the bad - but also the good things that the existance of the ring made possible) is dark and empty." It's something that we readers can relate to - the story has come to an end.

The question is: what does Tolkien tell us in his various stories, essays, and letters about the loss incurred through great and profound struggles--even when light triumphs over darkness. Is it possible to have the opposite outcome where "all is light and full of joy"?

I'm not sure I understand what you mean here. Are you asking 'can there be complete triumph without any loss and pain whatsoever?' or am I getting the wrong idea?