We cannot assume that angels are immortal and share the same kind of spirit God Almighty has; we cannot assume they are indestructible.
The origins of our adversary, Satan the Devil, and his host of fallen angels or demons. God has promised us protection if we yield to and obey Him.
Pride, vanity, presumption, and self-absorption led to Satan's demise. Satan's madness (that he is his own god) is the spirit of this world,