Well, we know that one day, God will put and end to satan by throwing him into a lake of fire and brimstone (Rev 20:10- and the devil who had deceived them was thrown into the lake of fire and sulfur where the beast and the false prophet were, and they will be tormented day and night forever and ever.) So inevitably Satan will be done away with. My best conclusion of why God still does allow Satan to run wild is threefold:
1. God is absolutely sovereign over all creation, and this includes Satan. We know Satan and his minions are quite strong and they do wreck havoc but, they are only allowed a certain amount of freedom. We also know that God has planned everything from the beginning of time to the end. Nothing can thwart His plans, and things are proceeding exactly on schedule. (Isaiah 14:24- The LORD of hosts has sworn: ‘As I have planned, so shall it be, and as I have purposed, so shall it stand)
2. We know this All things work together for good to those who love God, to those who are called according to His (God's) purpose. All the havoc the Satan has caused and will continue causing until the day set by God for his punishment, is working for God's glory. A perfect example, Job. Satan was bent on punishing Job and God allowed it, why? Look at how the story ends, God is glorified through that. Look at Jesus, He was crushed by the plans of Satan and sent to the cross. But God used that, and now the cross is a symbol of our death to sin, the grave our resurrection to life. So inevitably, Satan's rebellion serves God's purposes. So Satan's chaos cannot be used as an example to show that he overpowers God.