What would be the ball park figure life expectancy of inoperable aortic stenosis?

Depends on severity: Life expectancy is very hard to predict. But first we need to understand the type of aortic stenosis. Is this regarding a malformed aortic valve (i.e. Seen in kids) or an initially normal aortic valve that has degraded with age (aortic valves calcify, are damaged by atherosclerosis etc.). Knowledge of the type/mechanism of aortic stenosis and severity is required to estimate an answer.

More detail: There is not much "inoperable" as. However, the patients overall frail condition, such as in the very elderly with other health problems, or perhaps a very damaged and poorly functioning heart may make this too high an operative risk. But it isn't the valve. Per se, that is inoperable. Some folks would try a percutaneous valve placement in this setting.