God does not destroy what He creates. How do I know? Well... first of all He has given us a Natural Law which tells us He does not destroy what He creates; The First Law of Thermodynamics which states that matter and energy cannot be destroyed or created. Since time and space were created...
The purpose of the universe is to create beings that know and create. It is the nature of intelligence to create intelligence. As cold is the absence of heat and darkness is the absence of light, evil is the absence of good. We know from our own experiences that men do evil not for evil's sake...