Like others have suggested, there is a fallback just like in other systems, it's just not formalized - yet. The difference is that in government there must always be a fallback , while smart contracts leave open a possibility that in the future, with an ideally unhackable contract, the fallback can potentially be removed.
Sure there is. As the DAO hack showed us, if you can get enough of the network to agree to it, you can literally rewrite history and create an alternate universe where the contract never went wrong.
1) hacker steals massive amount of money from a crypto wallet
2) hacker cashes out and gets real money
3) network realizes the hack and "rewrites history" as if "the contract never went wrong"
How is this a valid outcome? Somebody in here is out a large amount of real money.
The hard fork may have been considered unfair by more people if the funds had not been locked, but the point still stands that if you could get enough of the network to agree with you, you can fork and start over at any block in the past you want.
Modern governments provide an elaborate system of fallbacks: checks and balances, a justice system with multiple levels of appeals. Those may be complex and fallible, but they are at least reasonably good at dealing with unexpected problems.
When a smart contract goes wrong, there are no fallbacks.