Amputation can sometimes shorten some peoples life expectancy depending on the persons age and current health and why they had to have a limb amputated.
For patients who had to have a leg or two legs amputated due to diabetes they may only live another 2 years to 10 years at most.
But if the person is older as in 70 years old or older then their life expectancy can be lower than some younger person such as 30 to 50 years old who had amputation done for diabetes.
If you're young and just had amputation done because your legs or other limb could not be saved due to trauma then you might live a normal long life but sometimes complications can happen but it's rare.
Still if you need to have amputation done you can live longer usually than if you had not had the amputation done.