aristotle - 4:05 pm on Jan 13, 2013 (gmt 0)
I remember a site that was shut down (run by somebody else) gradually drifted down the SERPS for several months before vanishing.
When you use the Google URL removal tool, as I did for this glossary page, it's supposed to disappear from the results in a day or so. In fact it did disappear from the "normal" search results within a day. But part of it is apparently still in the system somewhere, maybe in the Knowledge Graph, and still shows up in searches for definitions.
So evidently the URL removal tool only removes a page from the "normal" search results, but not necessarily from all types of searches.