From the article:

"In the last two years (2018 and 2019) — and funded purely by a few donations from friends and our own team — we have sent 4 backups to space.

    One is orbiting the Sun for at least 30 million years, in the glove compartment of Elon Musk’s red Tesla.
    One is orbiting the Earth on a satellite.
    One is now on the Moon for up to 5 billion years.
    And one was sent to space and returned to Earth and will go in a museum."

Telecom satellites in geostationary orbit will remain there on a geological time scale. Human civilization could knock itself down to a bronze age level of technology and rediscover spaceflight long before the orbits of any of them decay.

Some weigh as much as 6500 kg. Including a 100 gram library for PR purposes by a private satellite owner wouldn't be too hard. It's a lot less exotic than saying "the surface of the moon", however.

The Moon has a uneven gravitational field which can cause surprising orbital perturbations. There are some relatively stable orbits known, but it's a little unclear how stable they would be over a scale of many years.

Further reading: https://en.wikipedia.org/wiki/Lunar_orbit#Perturbation_effec...

What is the expectancy of a meteorite hitting this exact spot vs orbital decay?