I don’t know. I don’t dream of writing things that will last forever. I’m perfectly fine writing stuff that will be forgotten 5 years later. Posterity has no appeal to me, as long that some people read my stuff and like it and I touch someone with my words, I’m fine with that.
I hope that one day I’ll write something big/good enough that it will have fans, then they will write fanfictions of it and twist the story and the characters and create alternate universes etc.
And then I’ll go on the internet and read them all and delight in the way people play around with my story and my universe and my characters and laugh at the bad ones and the troll fics and enjoy the porn and the kinks and the AUs and life will be good.