That would assume that he could destroy all the organic life in Middle-Earth, or more importantly, that which exists in Tom's land. Certainly he would be devasted (emotionally speaking) if all the life in Middle-Earth were destroyed (except in his land), but it would only affect him in any significant way if his land was somehow damaged. Now, if Sauron (or anyone) somehow did destroy Tom's land, they would undoubtedly destroy Tom along with it. As in, Tom would likely perish as a result of the destruction, i.e. indirectly, rather than being destroyed directly.
However, I don't think that Sauron could destroy Tom's land. Sure, he could physically start pulling plants out of the ground, but I doubt that Tom would sit idly by and watch. I think it likely that Tom could cast anything and anyone out of his land (except, perhaps, the good Valar of Valinor), and there be nothing that person or thing could do about it. So though it's theoretically possible, I don't think it could actually be done.
Oh, and by the way, Shaber... Have you ever read The Death Gate Cycle? I only ask because of your title, avatar, and location remind me of it.
In my opinion.....
Tolkien threw in Tom as a sort of personification of himself and did not explain him to us on purpose. I like not knowing if Tom is a Maiar or anything else... He could be as powerful as Eru for all we know. There are soooo many theories about him in so many books. My theory is that Tom is Tolkien. He is a human character with great power, I think that he is truely good (or the ring would have had power over him).
Well, one thing that is certain about him is that Tom Bombadil and his donkey Fatty Lumpkin were originally from a children's story for Chris Tolkien, J.R.R.'s son. Tom Bombadil's presence in The Lord of the Rings is undoubtedly meant to be just something thrown in that has no ultimate affect on the story, except perhaps by providing a way for things to happen, such as the Hobbits' acquisition of the Barrow Blades. The fact that Tom is the one who gave them the Blades is insignificant, as Tolkien could have had, quite literally, anyone provide them with the Blades. Now, the identity acquired by Tom Bombadil as a result of Tolkien explaining his presence is what is truly in question. Tom has been, in a Letter by Tolkien himself, described as being a Maia. Whether he indulged any further information concerning Tom Bombadil is unknown to me, but there are quite literally hundreds of Letters written by Tolkien in response to questions asked by various people. It is likely that at least a few are about Bombadil, and as I do not myself have a copy of the book in which these letters have all been published (something like Letters From Tolkien), I cannot say for certain if any other information was divulged. Perhaps someone on this forum has this book? If so, they could provide further insight into this matter.
Here is a great link to read up on ole TommyClickyClicky
That article certainly raises some interesting thoughts and ideas. That he isn't meant to be anything is particularly interesting. An intentional enigma as mysterious as Tom is interesting to consider. He certainly is an enigma, no doubt about it, but the possibility that Tolkien left him as such intentionally is fascinating.
Well, I've always thought of him as being in-touch with nature (no doubt in part do to his ability to tell a tree what to do), so the idea that he's an embodiement of nature is appealing to me. But whatever he is, he is still one of the coolest characters in the whole The Lord of the Rings.
One idea that I just had, though, about Sauron: Sauron imbued the One Ring with a large portion of his power, which is why he diminished so drastically without it. Tom Bombadil went so far as to put the Ring on his finger, but what did it do? Absolutely nothing. In other words, the greater portion of Sauron's power and might had absolutely no affect on Tom. You might think that if Tom was weaker than, or even equal to, Sauron in might and power, then the Ring would have at least the slightest of affects on Tom. But did it? No, it didn't. Now, that doesn't necessarilly mean that Tom's more powerful than Sauron. It could just be, as I've suggested before, that Sauron's power holds no sway over Tom or his power. So even were Tom weaker than Sauron, not even Melkór would have any power over him. But that's just my speculation on the matter. Tom could just as likely simply be more powerful than Sauron, and there's no way for me to know any better.
Read this essay: Who is Tom Bombadil?
And this one: What is Tom Bombadil?