Yeah, I have at least one thing in my bookmarks that was hidden, so presumably still exists but no one can read it and I have no idea what it was. There is at least one thing in my read for later that was actually taken down. I try to download epubs of anything of decent length, but that only helps for stuff I was planning to read (or bounced off of), not for getting new stuff.
(I also never subscribe to fics or authors, because I'm a weirdo? maybe I should...)