It just seems to me that "cults" never really go away. When the founder(s) die, the organization moves forwards and progresses with changes. Often times splits occur, and the offshoots attempt to carry the torch of the founder outside of the organization he founded.
Since most cults believe they have the TRUTH, and believe that only a few make up the true church, growth is not an issue with them, as they believe they must decrease.
Christadelphians are splintered up into over a dozen schisms.
The Worldwide Church of God (Arnstrong) was never big to begin with (less than 100,000), they went mainstrean and lost about 80% of their followers, who splintered off into over 300 different groups, all claiming to pick up the torch of Armstrong. Just recently the original Church changes it's name from Worldwide COG to Grace Communion International.
The Mormons are the fastest growing religion today. They are splintered off into hundreds of smaller groups, today there are two main sects, the Church of Jesus Christ, and the Reorganized Church of Jesus Christ.
Even the Watchtower has splintered off. A few during Russell's time, a major split after his death, some during Rutherford's, and there continue to be some since 1931, continuing today.
Quite often, there are offshoots of offshoots of offshoots.
The only time a "cult" disappears completely is when someone is no longer able to pick up the torch and carry on. Even then there is always someone who has been influenced by them to continue another similiar group.
Sometimes a group dies off and a hundred years later someone finds his writings, accepts them and begins to restart the group.
RR