Physical casinos should really have an emergency kit and someone on standby that knows how to do proper first aid for people who will experience health concerns. Although it's not really mandatory for every establishment to have a medical personnel, I guess, but it's much better to have one just in case this scenario happens, especially casinos involve a risky decision that could make the emotions go rollercoaster causing sudden collapse and panic attacks.
As far as I know, they have this emergency staff 24x7 to help their customers in this kind if situations. I have seen some of them in physical casinos for emergencies and they are all competent to be a medical personnel. But as we have said, you can't control it, if it happens and they do the best they can and yet their customer succumb for whatever reasons, it's not the fault of the casinos.
It's just so unfortunate that the dealer didn't notice it easily. I bet if he knew, he would have called 911 immediately since cardiac arrest is a serious health condition that needs to be attended to ASAP. Perhaps they were oblivious since they were too engrossed and focused on the game. Somehow, the casino plays a fault on the death since they weren't able to notice and give first aid then call the emergency hotline. Hopefully, next time they will do better such as be more wary of the surroundings and the players behaviour so this won't happen again.
Yes, the dealer might not be notice it easily as for sure he is not to train to spot them. Of course, we wouldn't want to witnessed someone die on the table. But as I have said, if it's your time, then it's your time.