The data, which is text for the most part, is resident on unrelated nodes. This means that it cannot be erased. Once it is in the database, it is basically immutable.

The HIVE/STEEM fork exposed the weakness and potential immutability of Proof of Stake, in my opinion. Without new governance schemes, that are at this time unknown to me, Proof of Stake will always remain in the category of Utility Coins, not security coins, not anonymous coins and certainly not asset coins for wealth storage.