The solution to data longevity is such things as:
-Globally distributed storage
-Fragmentation and reassembly of data (so no host is responsible for content, since it is all just fragments)
-A protocol whereby the network monitors how many copies of a datum there are and creates more copies if it can't find enough.
-A protocol that automatically migrates data fragements to both newer host storage and more reliable host storage gradually over time.
-Re-wrappable encryption protocol
-Onion routing for access
-An economic model such as quid pro quo storage sharing (you store some of anonymous others' fragments, they store some of yours, no money exchanged.
-Storage of metadata and programming language execution environments and programs (with instructions) along with data