I know those coins are not actual coins, but just a entry in your internal ledger.
They are actual coins held in our hot and cold wallets. If someone withdrew them they wouldn't be there anymore. Whether or not an individual account with a balance is active or not isn't important but the overall size of the bankroll is.
The point of the bankroll is that we have coins available to payout if a high roller gets lucky. The maximum win is set to be a tiny fraction of the total bankroll so if someone wins it, even a few times in a row, we can payout without suffering a noticeable decrease in that bankroll. Over time the house will recover that amount when others come along and lose. So the bigger the bankroll the bigger buffer you have against a big winner. We don't "use it without the users permission" it's all just part of the big pot. Inactive accounts abandoned with balances make that pot bigger.
Yes jackg, if or when the site ever shuts down is the only time we'll ever know how much belongs to people that will come and collect it and how much is people that don't even remember having an account.