I don't believe God will allow Satan or Lucifer to kill 6.7 Billion peeople as this is even bold by Lucifers standards in history.
Know that before this occurrs you will see Damascus laid waste into piles of rubble then Christ will return and awaken all who are the dead in Christ and they will arise and all living who are the body of Christ will instantly be brought up into the clouds with Christ. The Rapture will occur so be ready for Christ to return as only God knows the day and the hour of the Messiahs return.