How long with an aortic stent last inside my body?

A long time. As long as there are no infections and the stent graft doesn't move, stent grafts are known to last for the life of the patient. Problems arise when the graft moves or the "seal" is lost and the aneurysm sac starts to grow again. This is why monitoring of stent grafts with ct angiograms or ultrasounds is very important.
Years. Need to follow up with your doctor to make sure that there is no narrowing or leaking from the stent / stent graft. Usually once a year enough. Report any new symptoms such as abdominal or leg pain.