John Mueller of Google said in a post on Reddit that disallowing Googlebot to crawl your site would not immediately lead to the site being deindexed. He added that "it would take quite some time for the whole site to drop out," and the home page may not be dropped at all.
So if you need your page or pages to be removed quickly, use the site-removal request in Google Search Console.
John wrote, "Even if you disallowed all crawling, it would take quite some time for the whole site to drop out, and likely things like the homepage would remain indexed. What you've posted here is IMO irrelevant. My guess is you did something totally unrelated, like submit a site-removal request for http:// (which removes all versions, as documented)."
You can learn more about all of this in this Google help document.
Forum discussion at Reddit.
