NDB Winnings that are not withdrawn

When a casino/bingo site offers a no deposit bonus, how is commission calculated if they win but do not withdraw the winnings? Does the balance expire after a certain time, and if so, are the commissions readjusted retroactively?

Lets say you have 1 depositing player who generates $100 in revenue, and 20 players who do not deposit who generate $100 in winnings between them. The net revenue would be $0. So what happens if nobody withdraws their share of the $100.

Make sense??