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Removing the pages will cause them to 404. Google will not instantly remove 404 pages, as sometimes website servers have issues and incorrectly return a 404 status on pages that are meant to be valid. As a result, Google will re-visit this page over a period of time and after seeing a repeated 404 is will remove it from its index. The easiest option to speed this up, should be to use Google Search Console "Temporarily Hide" option in Google. https://www.google.com/webmasters/tools/url-removal Pages will disappear quickly after using this and my guess is it won't come back if it's still returning a 404 status. If it's easy for you, you could turn the 404s to 410 (forever gone).