piatkow - 1:31 pm on Nov 23, 2011 (gmt 0)

Once Google have the page indexed it will stay indexed as long as it exists. If a link that no longer exists was spidered in the past or if it was in a site map then they will have found it and will continue to index it.

I have seen plenty of examples of orphaned pages continuing in the SERPS and plenty of webmasters who thought they were "taking down" a page by making it an orphan.