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In my experience, pages generally drop out in a month or so, but I haven't looked at this in a while.
Here's a discussion of ways to remove urls if you're in more of a hurry...
Fastest way to remove pages from google?
is it 404, 410, no index or..?
They do that just in case one day, they are no longer gone, but instead are republished.
Say you bought a domain name from someone and put up a new site. Say that Google refused to pick up your /about.html and /contact.html pages, and that eventually you found that it was all because once a page went 404 Google refused to ever look at that URL again.
You would think that was a bad policy. That is why it doesn't work like that.
To make a long story short:
If you want to get pages out of the index, you can't, and if you want them in, you can't either ;-)
Maybe you should try timing them out when requested or returning "500 Internal Server Error". That's what happend here.
You could also try to return "410 Gone" via htaccess:
RewriteRule ^path/to/foo.html$ - [G]