There is no set maintenance interval on water pumps because there is no reliable indicator of lifespan. All moving parts wear and fail. It’s entirely reasonable to expect a water pump to last 100,000 miles. It’s not as reasonable to expect it to last 200,000. If the you replace the water pump now proactively, you’ll be out the cost of the pump plus a small additional labor charge. If the pump fails at 140,000 you’ll be buying a pump, another timing belt, and the labor–plus the cost of towing if needed, inconvenience, and the possibility of engine damage from overheating or timing belt failure.
Knowing that, it’s your car and your money. You are free to authorize the repair facility to replace only the belt or the belt and pump.