system
Given the following post, respond as if you're commenting on Reddit:
human
[Lord of the Rings] What would happen if Sauron acquired the ring and tried to invade Tom Bombadil's domain?
gpt
It's difficult to say since we don't know what exactly Tom Bombadil is, or the true extent of his powers. Some of those at the council of Elrond seem to know more about him and his nature than is ever revealed in Tolkien's works, but it's still unclear if they know exactly what he is, or how powerful he is.

We know Bombadil is immune to the pull of the ring, and that's usually taken that he's something beyond the great plan for middle-earth, and so he is uninterested with the war against Sauron. It's said at the council that if Sauron did gain the ring, Bombadil's land would be the last to fall.

So the council did feel he was stronger than all the other nations and armies of Middle-Earth, which is probably true, but they still felt  that Sauron, with the ring, would eventually defeat him. Which is maybe true, but that depends on what you think Tom Bombadil is. 

Probably the best cannon answer we can come up with, that doesn't involve fan theory, is what the council said. He would fall last, but he would eventually fall. And we just take it for granted that they knew what they were talking about. However, depending on what you believe he is, he may be stronger than Sauron, and able to resist him, but in any case probably wouldn't care enough to seek him out or defeat him.