Do you mean that your hosting expired and your site is gone?
Did you create a backup when the site was still active? If not, you may not be able to get the files back.
It MIGHT be true that if it JUST expired (as in, yesterday, or last week), the files may still be on the server somewhere, but I would not count on it. And if it expired some time ago, I'm sure the files have been deleted from the server.