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In case of the 06-17 attack, this would freeze all ether in The DAO. The attacker, as well as anybody else, would not be able to withdraw any funds from any DAO.
Hard fork
The hard fork would mean rolling all the transactions back to a point before the theft.
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. But, as Patrick Murck, a lawyer and researcher at Harvard University’s Berkman Center says:
“The contract is the code, it's unstoppable code, it's unbreakable, it's self-executing and autonomous — right up until everything goes wrong. And then, 'No no no no, that's theft!' Which is some social norm that we've attached to it that's not based in the code, and then we're going to stop the whole system and basically bail it out. Is this something we're going to do every time a smart contract fails? Or is this just because there are a lot of [Ethereum] insiders in The DAO?"