URL lifetime... How long does a delinked URL stay in the index?

[SEOPTI]

If you delink a URL from your site so no link and PR points to this URL anymore, how long will it take for Google to remove this URL from the index?

I see if the URL is not set as 404 Google will probably never remove this URL from their index.

[g1smd]

There is a difference between the SERPs (the list of pages they show to searchers), and their database which holds a list of all the URLs they have ever discovered - and their current status.

A URL which returns 404 will usually drop from public view fairly quickly, but it may show as a Supplemental Result to allow people to still access the content via the Google cache for a few months.

Googe will revisit "old" URLs from time to time, almost forever, just in case the URL has come back into use.

[tedster]

Right - if the url continues to result in a 200 response it will stay in the visible index. If there is a 404 response, the url will leave the live index. Still googlebot will check for it for a long time (years) but on a declining schedule.