Normally, it should be reported to Anti money laundering authority so that this money will not cause them a trouble once the authority tracked the money of the illegal source. But I’m not sure if online casino practice this since they don’t have any physical casino while they operate internationally.
Maybe some of this illegal money will go back to their bankroll then just send to authorities when asked for it.
It don't have to be land based casino to comply with the regulation, if digital business can evade from regulation, SBF won't going to jail since FTX is just an online exchange. Sites that support or are illegal niches sometime get questioned by the web hosting, if you can't meet all of their request, they can shutdown your sites.
Well, there's a possibility they can use that money to add their bankroll because all the transactions are off-chain, just like SBF use his customers' money for investment.