Tax exemption on insurance

My friend has taken a life insurance policy. The policy documents state that income tax exemptions will be available at the prevalent tax rates. Does this mean that when the policyholder's nominee or the policyholder receives the sum assured or maturity benefit, let us say twenty years later, the exemption will depend on the law that is prevalent on that date? If on that date, amount received on life insurance is not exempt, the nominee or policyholder will not be able to avail the exemption?