Actually, I know some Christians who deny that everyone's soul is immortal. In fact, they have quite a few scriptures that they use to support their position, but it basically is based on the idea that an immortal soul was not a Christian concept originally, but rather a view based on Greek Philosophy. In fact, the argument is actually integral to an answer to the question 'Why would you want to become a Christian?', since it says 'because only Christians have eternal life (given to them by God)'.