How can you fault a guy who does what traders try to do every single day? The fault is only with Mt Gox here and this isn't the first shady thing they've done (apparently even changing jurisdictions to avoid getting sued over previous abuses). Mt Gox are scum bags and deserve to be shut down at the very least.
He writes he was aware that probably the hack is causing this and decided to take advantage of it.
He should give the BitCoin back to MtGox, who would then proceed to roll back the transactions. Simple as that.