There are several reasons for a cooling fan replacement, though under normal circumstances a cooling fan can often last the entire life of the vehicle. If a collision occurs the impact could damage the fan, usage can cause wear and tear on other components like belts, assembly house, motor, or relay and this normal usage can mean a cooling fan replacement!
More aspects to consider when assessing your cooling fan is whether it is manual or electric, whether the clutch is functioning, or if it is an electrical matter.