It may or may not be interesting to not that the "link rot sniffer" is not a single pass activity that forever bans a website that may have been down for the nanosecond when it was checked.
Robozilla makes multiple passes over a given category, and a site must be down for both passes -- not just one -- before the site gets moved to the unreviewed queue and marked red, so that an editor knows that a formerly listed site has gone unavailable.
Many editors make working with reds a priority. We check to see if the site has returned. We check to see if it falls into the "Geocities" model (sites get metered usage and towards the end of hte month may not be available due to bandwidth issues, but will be available again on the first of the month), we check to see if the wembaster has done something brilliant like changing the homepage from url/index.html to url/homepage.html or url/version2.html. We can't aways guess what a webmaster is thinking, but each editor has a handful of favorites to try -- especially if it appears the domain is up and running. We also go looking for replacement URLs. We check to see if there are any historical URL. We try lots of things before giving up on a URL, and many editors will "park" URLs someplace safe and come back in a month or two month, or six months to see if they have resurrected themselves.
