aakk9999 - 11:32 am on Jul 31, 2013 (gmt 0)
Personally, I would "do it the other way around", meaning serve a correct 404 or 410 header for the removed pages but rather than a generic 404/410 error page I'd grab and display the information that would be redirected to on the 404/410 page for visitor convenience. (..)
ADDED: I'd probably insert a "sorry, that page has been removed, but we've provided you with similar resources below." notice at the top of the error page so visitors know what they were looking for is not present, but there are other resources on the site they might like.
Yes, I would do this too, this would be the proper way. 410 Gone would be more appropriate response in this case.
This is completely unnecessary if the correct header responses are returned. Better test your response codes properly.
(I would also noindex the 404/410 page, just to be safe.)
As I said, I would send 410 instead, but in any case, as long as you are not internally linking to these pages you will be ok, the WMT "Not Found" section is for your information only.
What would be the impact on Google rankings when it suddenly starts finding a huge number of 404 errors.
However - one exception - if one of such pages to be removed has very good external links, then on some cases I may decide to leave this page returning 200 OK and add a disclaimer to that page along the lines that this info does not exist any more, please go to city URL to see the full list of currently available services.
But I would do this only as an exception if there is a really good external link to be preserved.