For what length of time can my dad live with 10% kidney function when he refuses dialysis and transplant?

Life expectancy: Tough question. A person can survive on 10% kidney function for a long time if managed aggressively with medical treatment. The caveat here is what caused the 90% loss of function? Under most circumstances, any fall below 10% creates a cascade effect that accelerates function loss to 0 and death and this can happen very quickly. I am being vague because i need more info to answer accurately.