[nuancebydefault]

In fact the blockchain cannot be broken because it is a chain. Compare it to git commits. If you would hack away one commit in the middle, the whole system would change. The other commits are comparable to any other transaction (ledger) that happened anywhere. As far as i understood, 'in blockchain' =='carved in stone' .

[lmm]

If people actually follow the rules they claim they do then yes. In practice once you ask them to put their money where their mouth is people make an exception. Again see the Ethereum DAO incident.