How would you prevent a rogue developer from updating/deleting events? Even if you could tell from the hashes that something changed, you would lose whatever data the dev changed. Backups can help mitigate this, but not until after the fact.
Have database replicas that only listen to INSERT statements (easy to implement in My/Maria SQL with BEFORE triggers), and design the software that works with the DB as append-only.
Right. Or any other append-only system, really. I mean, one wouldn't ask "how do you prevent someone from deleting an email they sent you earlier?"
The same way American Express, Visa, the Automated Clearing House and your bank prevent rogue developers from updating/deleting your money: With internal security processes, threat of termination and ultimately the legal system.
Not necessarily. Think of git. Git is not a blockchain. If a rogue developer deletes code and/or rewrites history and forces a push, I will know and can undo that rather easily.
Amusingly, that's because git is a merkle tree, which is one of the core building blocks (ha!) of a "blockchain" as it's used by "blockchain" enthusiasts.