What is the average lifespan of someone with aortic stenosis if not corrected?

Depends on symptoms: Patients with uncorrected aortic stenosis have a poor survival: half of the patients that develop angina (chest pain) will die within 5 years, half of the patients that develop syncope (passing out) will die within 3 years, and half of the patients that develop heart failure will die within 2 years. Aortic valve replacement can pretty much normalize the life span and improve symptoms markedly.