When anyone is allowed to redistribute under their own terms and attribution, what the user can or can't do depends entirely on where/who they got the work from. Which means in your case that if the place you published the work becomes inaccessible, for example the heirs or successors stop paying for hosting, people that got it from you using the hypothetical super permissive license might no longer be able to prove they are allowed to do what they want with the work.
That is "merely" a matter of record / archiving. I'd be happy to annotate my first-party copies with copies of the license, so there would exist copies of the work with the license / public-domain declaration attached. The authenticity could be attested by archived copies (perhaps held by Github, Wikipedia, the Internet Archive, or web scrapers / archivers like the WayBack Machine, Google Archive, etc.), or by being signed with a cryptographic key of mine.
This same problem exists with the public domain. If, in the United States, you find an unpublished century-old manuscript in your attic, its copyright has expired, and you can't claim rights to it. However, because nobody else knows about it, you could in practice type it all in to a computer and claim to have authored the work.
edit: This record also does not have to be perfect. I will probably be dead in a century and unable to care about, or further influence, the usage of my work. Under current U.S. law, my works will already be in, or eventually entering into, the public domain. If you really want to be long-term, there's no guarantee that in the distant future anybody will have a copy of, or care about, my works. Alternatively, there is no guarantee that, in the long-term future, the present state of intellectual property law, or any actions I take within it, will have any bearing on the rights future beings will have to do or not do things with my works.
