What if humans have long left the Milky Way galaxy
If out descendants become intergalactic spacefarers, then we probably won't ever all leave.
and aliens visit us then?
Those aliens will probably be our descendants. They'll just have to look up the information in their archives. It's not like keeping raw information is going to become so expensive, we have to delete it.
Imagine a universe so old and so populated that a good portion of the matter/energy available in the universe must be devoted to storing the histories of the various civilizations. Wars would break out over data resources, as factions war over access to storage and compute power.
That assumes a future where humans colonize the stars and spread life through the universe. What's more likely for humanity is a future more like the matrix, except instead of being enslaved, we place ourselves there willingly. It seems to me the focus of most of our technology has been to figure out how to poke and prod our pleasure sensors to maximum effect. Forget the stars, we're going to invent our own personal paradises on Earth and just stay here.
Imagine a universe so old and so populated that a good portion of the matter/energy available in the universe must be devoted to storing the histories of the various civilizations.
Perhaps by then, some very clever entity will have figured out a quantum computer implementation of The Library of Babel. It won't actually store all possible books, but it could be used to very quickly search the space by generating all remotely coherent possible books.
What's more likely for humanity is a future more like the matrix, except instead of being enslaved, we place ourselves there willingly.
Those aliens will be our descendants. And they won't have to excavate. They'll just look up the right shop in Akihabara, or equivalent of the time.
http://kk.org/thetechnium/technologies-do/