Well, I was open minded and I checked out the verses and it just doesn't add up, my friend.
First, Luke 10:18 is a prophetic vision of Jesus. For Romans 4:17 says,
"God, ... calleth those things which be not as though they were."
Also, Jesus prophecied his death and resurrection and the faling away of the disciples and judas's betrayal. In other words, just as Jesus was able to forgive sins before he went to the cross, Jesus was letting his diciples know that they have power to overcome the devil because Jesus (Who is God) has already seen His victory over Satan being cast down from Heaven in the future during the End Times.
John 12 confirms that Satan's fall is still yet future.
Now is the judgment of this world: now shall the prince of this world be cast out. And I, if I be lifted up from the earth, will draw all
men unto me." (John 12:31-32).
Second, if Satan had been cast down as the accuser of the brethren in Luke 10:18, then why does Jesus tell Peter that Satan desires to sift Peter like wheat in Luke 22:31?
Third, in Revelation 12:12 says that when Satan is cast out he has great wrath because he knows he has but a short time. If this was during Christ's ministry and or after his death and resurrection, I would say that 2000 years + is not a short time. Besides, Revelation 17:10-11 says that he that comes (the Beast) will continue a short space. This short space or short time is confirmed for us when the Jews flee to the mountains (i.e. the wilderness) for 1,260 days (Revelation 12:6) when they see the Abomination of Desolation in the Jewish Temple (i.e. When the Anti-Christ descrates the Temple and declares himself to be God). This is the 3 and a half years (Which is the final half of the 7 Year Tribulation, a.k.a. Jacob's Trouble or the Great Tribulation).
In fact, if you were to re-read Isaiah 14 and Ezekiel 28 where it talks about the Fall of Satan, you will notice that the language used to describe his fall (or casting out) from heaven is one that is still yet future. The devil's casting out from heaven takes place during the midpoint of the Tribulation, whereby he will make war with the remnant of the woman's seed (Which are the Tribulation saints who will be beheaded or martyred for Jesus).