you can sell coins at bitfinex or on USDT markets and hope the price disparity dies down, but that's about it. you can't actually withdraw USD and complete the arbitrage cycle.
This situation is scary. Mt. Gox closed withdrawls as well when they had problems. I hope bitfinex solves this situation fast.
supposedly they have. they said a couple days ago that withdrawals are now flowing without interference (though they admitted there was a backlog). and they've brought fiat deposits back online. this suggests they've established new banking relationships.
the price disparity between exchanges will tell the real story though.......
About arbitrage, it's possible when when market volatility is high. It's also possible if you have exchanges in different countries with different currencies, such as USD and some other local currency.
If someone manage to somehow have a South Korean bank account and a USD bank, it may be possible to make nice arbitrage with some altcoins which are more valuable in south korea.
it's difficult in practice. you need to open a korean bank account in person and establish alien registration. then you are restricted to $50k in remittances per year. and that's if you can even trade on korean exchanges---many only allow koreans.
i think that's why the korean price disparities often persist: because very few people can effectively arbitrage there.