Today, this is not an issue. It used to be the case, and for good reason. Imagine you had a small brokerage that needed to profit from trader losses. Then Joe Grind, this smart trader, keeps hammering you for hundreds of thousands daily, but to make matters worse, he cashes out immediately. You end up with lower revenue and negative P and L. These days, most brokers are well-capitalized and have many losing traders on their books. They need a 70% loss to keep churning, so out of every 100k deposited, they expect to keep 70k within 90 days. So it would not be an issue.

So, like I said, you won't get thrown out unless you make a mess without telling them first, in which case they can withhold the profit and have a chat. Some will apply a large swap, as it is considered arbitrage. So no, you will not be thrown out, but you won't get the money either. In most cases, you will. FXCM opted to go nearly broke paying clients; Alpari also did the same, so you have to face the reality that regulators give licenses, so if you don't play nice, you get locked out of the lucrative European markets.