Tone

[Tigerlily Gamgee]

This is sort of related to the "If feels different near the Shire" thread.
My friend and I were walking around "the windy city" this afternoon and we were discussing fantasy (and of course, Lord of the Rings).
A thought came to my mind...

What if Tolkien had not decided for the Fellowship not to be broken??
I mean, when looking at the books, the tone of the book changes so much when the characters are set out on their separate journeys. I think that the breaking of the Fellowship is what really starts these books on their main journey. Up until then the tale is still semi-light-hearted. I look at the The Fellowship of the Ring and compare it to the other two books and it can be easily seen how the tone and structure is different.
Do you think that Tolkien knew what was coming next before he wrote it, or was it as much of a journey for him. I have not read many of his letters, so some of you may be more clear on this than I.
I just thought how amazing it is that a choice like that is essentially what helped to create such an epic. Had the Fellowship remained together and had a nice, long, happy journey the book would've surely been labeled as a fairy tale.
Sorry if this seems a little strange for a topic to some of you... I was just wondering if any of you has any insight to this subject.