Here are resources about this topic:

• The Spirit World (Satan, Messengers, Demons) by Concordant Publishing Concern
• A study on the existence and nature of demons by Aaron Welch
• The Nature, Purpose and Destiny of the Adversary (Part One) by Aaron Welch
• The Nature, Purpose and Destiny of the Adversary (Part Two) by Aaron Welch
• The Nature, Purpose and Destiny of the Adversary (Part Three) by Aaron Welch
• The Nature, Purpose and Destiny of the Adversary (Part Four) by Aaron Welch
• The Nature, Purpose and Destiny of the Adversary (Part Five) by Aaron Welch
• A defense of the doctrine of Satan’s superhuman, spiritual nature, and a response to objections by Aaron Welch
• Bible Student’s Notebook 854
• Will Satan be saved? by Scott Hicko