[earlz]

This has happened with other, much smaller, cryptocurrencies. The choice usually agreed upon by exchanges, developers, and community is to pick a known good block before the attack and fork the chain backwards from that point. It requires significant downtime and is of course very complicated, but several different cryptocurrencies have used this method and recovered to a functioning blockchain

[once_inc]

> several different cryptocurrencies have used this method and recovered to a functioning blockchain

The most notable is Ethereum, with the DAO hack and the subsequent bailout. Did lead to Ethereum Classic, which is a fork that gained some traction.