I would have answered as I honestly believed as a Dub, that God can read hearts and would only put to death those who would never live a moral, Christian, life.
This would beg another question, if God reads hearts, then He would know that some of those in field service are not pure of heart. If that is the case, then some JWs would be killed and some non-JWs would not. Which would imply that being a JW is not needed to be saved from Armageddon, only living a moral Christian life. This would actually be perfered (if you ask me) because that is the standard from which God judges us (according to the logic I just made up).
But of course I believe that we are saved by faith through grace in the living Son of God as outlined in Acts 16: 30-31