Not true. I had a buy order in around $12/btc that triggered on the way down and I was able to withdraw my BTC before the site shut down. I'd like to know how they plan to roll THAT back.
The way they'll have to deal with this is not roll back the buy-side of a transaction if it was withdrawn. Roll back the sell-side and cover the difference. I.e., if market price is 17 and you bought at 12, MTGOX will have to refund the BTC to the rolled-back seller from the MtGox stash or, if stash is too small, add $5 per BTC to your $12 per and buy them back on the open market then refund to seller.
No doubt some buyers withdrew, but if it isn't a huge percentage then MtGox should be fine to cover the loss from the fees its collected so far. But we'll see what actually happens...