It's never going to be like that. In the past, there was absolutely no sure way to preserve information. Stone tablets and 2,000 year old scrolls happen to be fragile. On top of that, things had to be manually chiselled or written out, copying from preexisting text or oral records, massively limiting the availability of information that wasn't oral tradition.
Now everything is saved on the internet. We have literal digital copies of nearly every literary work or record on the planet. In order for that to disappear, you'd have to destroy every major city and server hub. At that point, we'd probably already be extinct.
Also, more importantly, though archaeological mix ups do happen, researchers tend to be pretty good at determining the context of a lot of works.
eh but to say if we did get wiped out some other species might come along evolve and become the intelligent life form
In which case, their archeologists would probably realize it was a work of fiction; you know, like how we don't form religions around Robin Hood or Gilgamesh.
said intelligent life might not be that intelligent yet. and those are known works of fiction. (not so up to snuff on my knowledge about the tale of gilgamesh) but all it took for the human race to be swayed was someone saying they spoke to god, and wrote a book on it.
better argument would be is almost none of our religions are based on scriptures we found buried somewhere.
So how are they not intelligent enough to understand fiction, but are intelligent enough to read the language of an extinct species?