If they go into the cove and is killed, how would the others know that going into the cove is dangerous? There are plenty of examples of human beings dying in

If they go into the cove and is killed, how would the others know that going into the cove is dangerous? There are plenty of examples of human beings dying in their home and no one noticing because they aren't missed by anyone. The same would happen if an entire social group of dolphins just disappeared. I think you're being a bit unfair to the dolphins here.