If they invent a cure and it's forgotten by future generations, then it is a failure. If their cure is remembered and passed on, then their memetic output is n

If they invent a cure and it's forgotten by future generations, then it is a failure. If their cure is remembered and passed on, then their memetic output is not lost, so they contributed - just not genetically. Sure genetic material can survive where culture and memory is lost, and evolves more slowly, but cultural contributions do shape the future a lot as well.