Cardiac Stents do prolong someones life as the cardiac stent when put in place helps to prevent future heart attacks, strokes, blood clots etc.
However still you can have a heart attack even after having a cardiac stent put in place so the cardiac stent doesn't guarantee no heart attacks or strokes but you have less of a chance of having another heart attack or a heart attack at all after having a cardiac stent put in place.
You still need to watch what you eat and exercise when possible to keep your heart healthy and prevent future heart attacks.
But the cardiac stent when put in place helps to keep you from having another heart attack or dying sooner.
Most people who have cardiac stents or other stents put in place live out a long healthy happy life.