Nebulous "It" and Absolutes

[Firefoot]

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 don't think it is. In any of the great struggles or conflicts there was at least some loss. On an even broader scope than just Frodo, in the War of the Ring think of all the losses there were. There were several people that died, for example Théoden, Hama, Halbarad, and many others. Arwen became mortal and the Elves passed away into the West. In all that suffering, victory is at best bittersweet. It can't be truly joyous because of all the loss. How can anyone come away unmarked or unaffected from a war or other bitter struggle?