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But even if your site isn't in the index, folks can still follow links from other sites to yours, and they can still access your site directly by typing in the url, if they know it.
<edit>Of course, that was a down server, so the IP address was considered "dead" as far as Google was concerned. That may have been part of the problem as to why the site disappeared.</edit>
They've got some good info on the differences between what happens during crawls, deep crawls and updates.