Luckily I never had that problem with bookmarking because I use firefox's bookmarks instead of ao3's out of habit and because it's more practical to keep all my bookmarks (sites, fics, mangas, art) all in one place that is also easy to backup, which is why I still have the bookmark and could find the name of the nuked fic I mentioned previously to check if someone had saved it. I'm also lucky that I save the fics I like and upload on drive as backup, so I still have those 10 chapters I read despite it most likely not existing on the internet anymore.
The author of that Zelda fic is really insane, if she wanted to put a fic behind patreon why not write a new one? Even without that crap, if someone decided to rewrite a 500k words fic to "improve" it, you can bet your ass I'm dropping that shit, the time wasted rereading their improvements would be better spent reading other fics.
This reminds me of a fic I read, it was around 13k words I believe, it was supposed to have three chapters, I normally wouldn't have read it because it was threesome, but I made an exception that one time because the summary interested me enough, then at the foot notes the author said they weren't sure if they were going to continue the fic, I don't remember why, because they were insecure or something who knows, point is they could've said that on the head notes and I wouldn't have wasted my time reading it, I was so incredulous with that bullshit that I could only laugh.
Regarding nuked stuff though, it sucks that we need to save and backup pretty much everything on the spot nowadays just in case it gets nuked, which doesn't help when I'm waiting for a long multichapter fic to be completed before I read it, though nowadays I don't read as much as a few years ago and I'd rather not even start before it's completed, so that if it gets nuked I'll feel less disappointed.