If a Japanese or American court orders MtGox not to enable withdrawals of BTC or fiat until they can prove they can cover all customers' deposits, then that is what MtGox will do. Someone just needs to convince a court to make that order. I would be shocked if a good lawyer couldn't make that case given that the collapse in price on MtGox is universally attributed to fear that they're not solvent.

As I said further up the thread, this is the clean option. The messy option is that USD holders get cashed out, MtGox declares it can't cover BTC deposits and becomes insolvent, and then everyone who withdrew fiat becomes a target for clawback based on the principle of unfair preference. If you're a USD holder, do you want to face a lawsuit or multiple lawsuits from the BTC holders?