The Internet Archive would not require the Internet to continue to store digital data, nor to ingest additional digital data. As long as the bills get paid and people watch the machine, the data would remain on disk and accessible.
The Library of Congress has existed for ~225 years, for example.
One requires more electricity than the other, and custodians of somewhat different skills. A sysadmin is a librarian and custodian with technology skills. If you can vault and custodian physical archives at scale, you can do the same for digital data (imho, based on experience with both). You’re simply building resilient systems on durable primitives.
I’m hopeful for a future where you can potentially carry all recorded knowledge on a device and media you can fit in something somewhat human portable [1]. But until then, humans interested will maintain and continually improve archival and information retrieval systems to preserve and make accessible knowledge.
The Library of Congress has existed for ~225 years, for example.