How Can a PoS Network Recover from a Successful 51% Attack through Social Consensus or a Hard Fork?

If a PoS network suffers a successful 51% attack, the community can coordinate an "out-of-band" recovery. The primary method is a user-activated soft fork or a hard fork.

The community of node operators, developers, and users can agree to adopt a new version of the software that effectively ignores the attacker's malicious chain and slashes their entire stake. This "social consensus" acts as the ultimate backstop, allowing the honest majority to essentially vote to invalidate the attacker's actions and eject them from the network, thereby restoring the integrity of the ledger.