Just the Russians closing their doors and leaving with your BTC a la Sheep Marketplace style. Or someone closing their bank account etc... with the same results, without any known person or company to follow. People bitch about Gox (and for good cause) but there's a reason that it's the only place where all of the big whales play at and every other exchange follows. Even after stopping all USD withdrawals, and a month SEPA withdrawals they're still like #1 (or so) exchange, think about it