This is non-starter, I'm afraid. The way insurance policies work is by assessing risk. Risk involves the probability of something happening - in this case you are presumably asking about life insurance, which is paid out upon death of the policyholder.
The insurance company takes a view on one's life expectancy based on a series of factors - questions they ask about one's circumstances and lifestyle.
If you are already ill, they are very likely to want to exclude death from this illness from the policy.
If they are able to include the illness (and it is life-threatening with a life-expectancy of between 5 and 10 years) they will structure the monthly premiums such that after about 6 years you will have paid out in premiums what your dependents would get in returns on death.
That's the way it works - die early, you might have gained a bit - live a bit longer you would have paid out more in premiums than is returned to your dependents.