If you requested a withdrawal anytime after July 1st you can cancel that request and sell your BTC elsewhere at a premium probably.
No, because if you cancel your withdrawal request you still have only USD or EUR in you account - and not BTC.
You'd still have to exchange USD -> BTC on MtGox before you can move it to another exchange.
Yes, that's my point. You cancel your withdrawal request and get USD/EUR back into your account. You then buy BTC and move BTC somewhere else to sell. Before it made little sense to buy an asset with falling price, but now the price is rising and it's more favorable to own BTC.
If you need the fiat, and you can withdraw either JPY to a Japanese account or EUR to an account within SEPA (EU + EEA + Switzerland and Monaco), you should sell at MtGox and withdraw from there. The price is better there than on all other exchanges.