You have to wait till the coin of your ICO to hit the exchanges and trade your ICO coin to BTC. After that use an exchange (eg. coinbase) to sell BTC for fiat.
Alternatively, you can post in marketplace to exchange your ICO coin for fiat with another member here. Remember to use escrow for such trades.
Thank you for your response, but I think you're missing my point..
If
MY ICO was successful and I have $40 million worth of Ether, how can I withdraw this to fiat currency?