Every single thing I've ever posted is immutably maintained. Steem (in my opinion) renamed to Hive in HF23 and defended itself very well from a very serious and well-financed attack made possible by the ninja mined stake and the centralization of Steemit, inc. Both of those things do not exist on Hive.
That said, there are still improvements to be made to further secure Hive and prevent this from happening in the future.