This is interesting. I have tried to do a little digging over the last hour or so and have came up with several items that may interest and be educational to the readers here.
I believe one of the main questions is why has God allowed Satan to continue to exist? Since he is discribed as “a murderer” (John 8:44), why not simply impose on him the same death penalty that civilized nations have imposed on murderers from time immemorial (Numbers 35:16)? What possible justification could God have for allowing one so wicked to continue to live?
The answer, I am convinced, has to do with the nature of God, and the nature of the spirit beings (angels) that He created. Consider the text of Luke 20:33-36. Within this passage, Jesus spoke of the righteous who one day would inhabit heaven, and stated that “neither can they die any more, for they are equal unto the angels.”
If righteous humans who will inhabit heaven cannot die, and if they are equal to the angels, then it follows logically that angels cannot die. While the Godhead is eternal, humans and angels are immortal and this would include Satan prior to his fall.
Why did God not destroy Satan when he sinned? Why let Satan continue to exist and influence others to sin? I think the answer here lies in God’s nature—his eternal nature which he has passed on to angels as well as to men—for there will never be a time when the spirits or angels, the evil as well as the good, will cease to exist. Punishments and prescribed limits have been passed upon evil spirits, and the more will be passed upon them, but they will always exist.
Scripture portrays angelic beings as immortal, whether righteous or sinful they will never cease to exist. However, there may be more to Satan’s continued existence than simply the angels’ immortal nature.
The reason might be expressed in the words the Lord asked Moses to say to wicked Pharaoh: “For by now I could have put forth my hand and struck you and your people with pestilence, and you would have been cut off from the earth; but for this purpose have I let you live, to show you my power so that my name may be declared throughout all the Earth” (Exodus 9:15-16).
From man's point of view, the continuation of evil, even for a brief period, generally is not viewed as either desirable or ideal. God may have “allowed Satan to retain his power, temporarily, until he is through using him to test and purify a people for his ultimate glory and purposes”. Certainly, God’s glory was exemplified by mankind’s creation because Isaiah, speaking for Jehovah, said that man was “created for my glory” (Isaiah 43:7).
I believe the Scriptures reveal enough information for us to conclude that Satan’s continued existence follows logically from the immortal nature of angelic beings. They also reveal that the devil’s existence is not at variance with Heaven’s eternal plan, since at times it affords opportunities for man to witness the working of God in front of His creation.
There is much more that can be said about Satan. If someone has a question I will try to find an answer.