This is something that keeps me worried at night. Unlike other historical artefacts like pottery, vellum writing, or stone tablets, information on the Internet can just blink into nonexistence when the server hosting it goes offline. This makes it difficult for future anthropologists who want to study our history and document the different Internet epochs. For my part, I always try to send any news article I see to an archival site (like archive.ph) to help collectively preserve our present so it can still be seen by others in the future.
I’d argue that it can help or hurt to decentralize, depending on how it’s handled. If most sites are caching/backing up data that’s found elsewhere, that’s both good for resilience and for preservation, but if the data in question is centralized by its home server, then instead of backing up one site we’re stuck backing up a thousand, not to mention the potential issues with discovery
