Board Thread:Lore/@comment-25124648-20151002000823

When the hobbits return to the Shire after their journey to Mordor, Gandalf leaves them close to Bree and goes towards Bombadil’s country to have words with him. We do not know what they say. But Gandalf was sent to Middle Earth to contend against Sauron and now he must depart. He has been given no mission to confront Bombadil and he must soon leave Middle Earth to powerless men and hobbits, while Bombadil remains, waiting to fulfill his purpose.

The spell that binds Bombadil to his narrow and cursed country was put in place centuries ago by the Valar to protect men and elves. It may last a few decades more, perhaps a few generations of hobbit lives. But when the last elf has gone from the havens and the last spells of rings and wizards unravel, then it will be gone. And Iarwain Ben-Adar, Oldest and Fatherless, who was ruler of the darkness in Middle Earth before Sauron was, before Morgoth set foot there, before the first rising of the sun, will come into his inheritance again. And one dark night the old trees will march westward into the Shire to feed their ancient hatred. And Bombadil will dance down amongst them, clad in his true shape at last, singing his incomprehensible rhymes as the trees mutter their curses and the black and terrible Barrow-Wights dance and gibber around him. And he will be smiling.

This is from a theory on a website. It's not the whole article, but the whole article has lots of evidence for this theory. The True Story Behind Tom Bombadil.  