Ethereum will continue to slowly bleed out over next 26 days until the "stolen" ETH is available to be spent. The big bleedout will occur when one of two things happen:
1. Ethereum forks, either soft or hard, both would be disastrous to the long term viability of ETH. It would be a very dangerous precedent to set.
2. No action taken, the "stolen" funds become spendable and the attacker dumps them all on the market, because who the hell wants to sit on several million dollars worth of funny money?
Either scenario would involve a mass dump return Ethereum back to sane pricing. Over 1 billion market cap for an unproven system was always unsustainable, this just hastened things along. I would not be surprised to see it go under $1 or $2 after all this is said and done. Ethereum still has a long term chance if they do not fork, though it will take a long time to recover from this market shock.
Why do they fail if they fork?
Seems to me the fanboys who buy anything that sounds good, don't really care about whether it is decentralized, because we were writing for months in the Ethereum Paradox thread that Casper would be moving it towards centralization. They only believe what they want to believe.
So why would recovering the funds for the fanboys be worse than not from the perspective of sustaining Ethereum?
They can state that the rules weren't well elucidated and that in the future, all users must understand that contracts are not warranted to perform as advertised.
Tual has potentially a big problem if they didn't do adequate disclosure. This can end up in lawsuits and he can end up prosecuted under securities regulations. If they did make very clear and conspicuous disclosure about risks, then they definitely shouldn't fork because no one will ever again know what the rules are (as they will be open to change at-will).