I have deleted some pages completely and have replaced them by new pages. This is a good reason to run a 301 redirect, since this is a permanent change.
I figured Google finds those redirects quite fast and replaces the old pages by the new ones quickly.
Now if the pages would just be deleted, without setting up any redirects on the server, without having them in the robots.txt, just plain deleted: how long until Google figures the pages have gone and deletes them from the index/SERPs?
Right now that might be tuff to say, but was has it used to be? Might depend on how often Google visits the site, let's just assume there used to one or two visits to this particular pages every month.
Will the guessing go from 1 day to 1 year or can anyone be more specific?
I always seem to get shot down when I state that Google contains a lot of junk from several updates ago but I'm convinced there are still some old pages in the serps and it has nothing to do with my server, it's Google's index.