my moms left leg has no circluation

Hello and welcome to e health forum.

It is difficult to ascertain the life expectancy of a person with peripheral vascular disease, resulting in a nonviable limb.

It mainly depends on the primary cause of vascular insufficiency.

There are other risk factors and medical conditions (including diabetes, hypertension, renal status, infections, current physical fitness, etc) that have to be taken into account. In case there are multiple risk factors, then the life expectancy without proper and definitive treatment, will be reduced.

You might consult with a vascular surgeon, who can examine your mother and provide you with effective answers and clear all your doubts.