If you deposit in dollars can you ever withdraw in bitcoins??

Or do you have to totally flush your account of dollars and start fresh?

Depends on the book. You can with some of the books. The smaller books mostly will not do it. Some of the bigger books say you can but will only do it for certain customers. 5Dimes will do it. Bookmaker is a maybe. 

Bookmaker is a yes. I do not deposit bitcoin but get bitcoin payouts.

Thanx.