I don't think there can ever be a total victory for one side or the other. The best we can do is a balance, where the forces of evil are neutralized.
The yin yang, as it is referred to in Western society, is an illustration of the constant movement and counter-movement of positive and negative energies. So long as they are in balance, we can continue to function.
For you nerds in the crowd, a better example would be the episode of Star Trek when Captain Kirk was accidentally duplicated in a transporter malfunction. His positive aspects were beamed up in one version of him, and his negative aspects than the other. In the end, it turned out he needed both to be an effective captain.