If you win a large sum in an unlicensed casino, then no one will pay you anything. Sometimes it is easier for a casino to create a new website than to pay large winnings to players.
Even a licensed casino can turn become a scam casino and they will not pay you, almost of licensed casinos in this forum are using Curacao license, Curacao license is weak and they're not protect the gamblers from scam casino. You can try to make a complaint to the Curacao license and then look how will they do with your case, I believe they will not handle your case, after all you can only hope the casino's owner to pay your winnings.
All casinos use the Curacao license because it is the easiest to get. Yes, the license does not guarantee that the casino will work honestly, so you need to study other factors, such as user reviews, reputation, how long the casino has been operating on the market. If the casino is fraudulent, it will not work on the market for 10 years.