Paul wrote that we wrestle against the 'spiritual hosts of wickedness in the heavenly places' (Ephesians 6:12). This shows that the devil and his host of demons still operate in the heavenly realm. When Jesus said that He saw Satan fall like lightning from heaven, He meant that He saw him fall from his exalted position, not all the way out of the heavenly places. This has not yet happened.
Revelation 12:9 says, 'So the great dragon was cast out, that serpent of old, called the Devil and Satan, who deceives the whole world; he was cast to the earth, and his angels were cast out with him.' This is prophetic of a future event. Verse 12 says, 'Woe to the inhabitants of the earth and the sea! For the devil has come down to you, having great wrath, because he knows that he has a short time.' This will happen at the end, about three and a half years before the return of the Lord Jesus. This is the time when the people of God will be greatly persecuted and the Antichrist will rule the earth. This is a time when all believers will need great faith.