This is more or less a solved problem. Tamper-resistant/tamper-evident datastructures like blockchains and merkle trees make it fairly hard to make things vanis

This is more or less a solved problem. Tamper-resistant/tamper-evident datastructures like blockchains and merkle trees make it fairly hard to make things vanish without a trace. You dont need all of the Nakamoto consensus machinery of crypto currencies, you just need your central authority to publish the latest hash on a ~daily basis.