With our technology, I really doubt the developers won't notice easily a discrepancy and sudden difference in their system. If their developers and security management team are always looking at the activities of their site, surely they would notice that there are glitches and errors from the system which people are abusing. Although it would be very unfortunate if the security team isn't really paying attention to details because like what you said, it could lead them to loss of profits, most especially if the abuse of the systme glitch was unnoticed for a long period of time.
This is why it is really important to keep the servers and security measures up to date. One must not be complacent because sometimes there are really errors even though you've already looked upon several times. Having a good team to examine every activities per day is necessary to secure the casino's functionality and security from possible abuse.
If they are attentive and have some kind of monitoring software apart from hiring a good amount of people to watch the site then it will be fixed as soon as possible but if not then those who discovered the bug are lucky that they can still withdraw what they have got and they can abuse it again and again until the admins will finally notice it. They can lose money on this tragedy but they should not lose hope easily. They can try to continue the operations and hope that they can run smoother this time.
This is still a gambling site and they have an advantage over the players. They can surely recover what is lost and they can earn more than that.
Hackers are always a head of what developers think. So even if you think you have secured your website. You can't be sure what loophole you have left.
So be vigilant keep the data safe and play safe. You never know when is the trouble knocking at the door?