That's subobtimal as well. The site could come out with a new robots.txt file which is just <code>User-agent: * Disallow: /</code> and everything already indexe

That's subobtimal as well. The site could come out with a new robots.txt file which is just <code>User-agent: * Disallow: /</code> and everything already indexed by the Internet Archive is now inaccessible to you.