The longest a person is likely to live after their kidneys fully shut down is 3 weeks and 4 weeks if they are lucky.
Most people who's kidneys have shut down and they don't get dialysis treatments die within 2 to 3 weeks of the Kidneys shutting down.
But if the person gets dialysis treatments they can live a normal long lifespan however some people die after a few years of being on dialysis treatments.
But some kidney patients have lived as long as 25 years while on dialysis but it depends on the persons current health and whether or not they miss dialysis treatments.
If the kidney patient misses some dialysis treatments then they could reduce their life expectancy as it's very important to keep going to the dialysis treatments.
In the case of renal failure the renal function declines rapidly within hours or days giving rise to serious metabolic disturbance and if that continues the person is no longer producing urine, which is known as oliguria and then it is unlikely the person would live longer than 3 weeks.