I think it's too early to say whenever Blockchains will replace notaries or simply remain as an alternative solution. Despite Blockchain's promise of eliminating the middleman, it's still not 100% efficient. One way or another, human interaction is required to make it work as intended. The main issue would be changing documents on a daily basis due to the Blockchain's immutable nature. You cannot do this without sacrificing decentralization.
You do not need to erase the document, you simply need to update the document and the changes will be visible and you can view the old document and the new changes and that is how a document should be as we should be able to verify all the changes made without erasing its history especially government documents, but it will take a long time to see changes like these.