be a Good human , Help the site find that bug and if they send you cash then thank
you but if not then just think of it as a act of kind since this is New Year mate.
also if you think they are not paying then leave it, let them find that bug so you have no problem.
There's no need to pressure him of that "be a good human" phrase. Let him decide, it is not his responsibility too. If ever it it really an important bug to be fixed immediately, I think that the casino should consider compensating him for the effort he did, if and only if he didn't exploited it beforehand.
It is still depend to both party if one would choose between to let the casino know or not. And if the casino would compensate or not. I'm sure though that the casino will give some reward if they think that the issue is major or critical.