That depends on the mollusk, really.
Akoya shell will always die. The shell is used (in most cases) for MOP, buttons, and "pearl" powder products. The abductor meat is eaten, raw in Japan as a delicacy, and sauteed in China.
Freshwater mussels do not always die at harvest. They are often returned to the water to produce a "keshi", or returned with a nucleus. Freshwater mussel meat is not eaten by humans, although it is consumed by animals. The shell is used in much the same way as akoya. But in the freshwater producing areas there are mounds of shell lying around. It is collected, but slowly.
South Sea and Tahitian mollusks do not necessarily die either. They can be renucleated up to 3 times. When the mollusk dies, the meat can be eaten (a delicacy in Australia), and the shell is used in buttons, MOP, tiles, jewelry, etc.