And that does not make the news, so we are not as aware.

Or, worse they get so large that they become institutions and don’t fear losing members any more.

a weakened cult without a clear leader will usually try for a while to cling to its identity, perhaps turning the missing leader into a martyr figure.

Brainwashed people don't deprogram easily.

It happened with the Mormons, and the Scientologists are trying to make it happen for them.

They are also a cult group, and they are spread all over the world.

Some age out. They literally die away.

Others continue until the divergence between belief and reality becomes too great. These have various endings.

A few sort of explode when the discrepancy is too large. "You said we'd be raptured/given power/destroy the enemy on this day, you were wrong." "I had the date incorrect. Forgot to account for the dilusionary transcentalist constipatio of Mercury's retrograde motion with respect to the Sacred Horde congregating around the Horn of Dilemma near the Sun's magneto-spiritual East pole." "That's what you said the other 23 times. We quit." Suddenly there's a congregation of one.

Or a new leader comes along, or somebody else rises to a position of some authority with Dear Leader's permission, and starts things changing to 'reform' beliefs to keep things humming along. But with no real reason to hang in there, most members just leave. Those who still believe also leave, but form a daughter cult.

Some just double down. "We must be even more righteous." They grow smaller, but carry on carrying on. Some continue to attract adherents and maintain a kind of homeostasis between losses and gains in population.

Some abstractify the problem. "We were right, but only on the spiritual plane." They grow more diffuse, but a lot of modern "spiritual" movements are like Theosophy--wackadoo from the get-go, but trendy and popular because trendsetters adopt them and the popularity-seeking brainless go a-lemming behind them.

At the national level some go to war. Nazi Germany.

Or, again at the national level, they simply collapse. The USSR. Many have claimed "we were right, but only on the social-justice plane" for this. Or have said, "We must be even more righteous."

And some commit suicide. Pol Pot's regime.

Some countries reform but keep some outward signs. The PRC, for instance. Vietnam.

And some explode. Syria, for instance.

Some double down on oppression, since they can enforce borders. PRNK, for instance.

Thanks. You got me thinking about this.

You had me howling with laughter here
"That's what you said the other 23 times. We quit." Suddenly there's a congregation of one.

Reading the first few responses really makes me appreciate your question!

How donnie is immune to truth is a mystery to me.
Maybe he has been so far away from normal that the light can not reach him.

in this age, the teens, mostly because they want an education. They are tired of being told they are going to hell for getting one. The young adults want high paying jobs with advancement and benefits. And both of these includes girls, which so often given no choice in their education.
Another big reason more are walking away now, of course, the internet. They found out the world isn't as Daddy and the Preachers said it was.

this was a fantastic 6 part documentary (on Netflix currently) about Bhagwan Shree Rajneesh and his followers who overtook a town in Oregon in the 1980s.

as to its ending (from The Guardian)

The Osho movement today, 28 years after its founder’s death, is a more tempered version than in Oregon, and focuses on selling books and meditation retreats. Yet it is still unwilling to accept the findings of the documentary. The Osho Times, its official organ, says the documentary fails to show “this was a US government conspiracy, from the White House on down, aimed at thwarting Osho’s vision of a community based on conscious living”. Even in death, Rajneesh continues to manipulate his followers