Is your Steem already in your Bittrex wallet? Or did you transfer it while the wallet was closed? If it is in Bittrex, sell it for BTC and move that to wherever you want - if it is in transfer, not much you can do until they enable transactions again. For the stuff that you are powering down, you don't have to send it to bittrex - instead binance, huobi, ionomy, and probably others have Steem enabled.