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Basically, it requires only the acquiescence of implementors and miners and need have no long-term repercussions, neither in terms of the code-bases nor in terms of the protocol spec.
In case of the 06-17 attack, this would freeze all ether in all DAOs using DAO framework. The attacker, as well as anybody else, would not be able to withdraw any funds from any DAO.
Hard fork
Move all funds from contracts with the code hash 7278d050619a624f84f51987149ddb439cdaadfba5966f7cfaea7ad44340a4ba to a new contract “RefundDAO”, replace the contract at the main DAO with a simple refund contract with only one function.