Generally when items are "taken down" from the Internet Archive, they just stop being published, and are not deleted.

I don't think it's mentioned in an official document, but it's usually referred to as "darking".

It probably safe to assume that the same concept applies to the Wayback Machine as to the rest of IA.

Edit: Here's a page that indirectly conveys some information about it: https://archive.org/details/IA_books_QA_codes