If I were Mark, I wouldn't allow people to withdraw money for a while. I would invoke security etc.
On an emotion-driven market like this, a bank run is the last thing we need...
If he only allows bitcoins to be withdrawn, it would make scared users to buy coins and run with them in order to minimize their losses.
Bitcoin would go up
and MtGox's losses would go down...
Obviously, Bitcoin is not for the faint at heart