Not sure either if they could still recover it or could even refund it but you should inform the team regarding the problem so they can do something to solve this issue. Same thing happened to me before when I sent the wrong currency to another network and it took a long time before I got refunded which isn't a bad thing since the mistake was on my end. I hope we can learn from this as well.

I once sent ltc to a btc address by mistake.
And guess what? The casino was able to get my coins back.
In your case getting access to usdt shouldn't be that hard, it all depends on the casino.
Good luck.