At this point in my life I have seen many religions go from being important in the United States to virtually non-existent.
That leads me to ask the question: ‘Which religions are likely to survive in the next hundred years?’
By watching the patterns of religion in the United States, where they are abundant, and watching the non existence of religion in Europe where they are state sanctioned, we can draw one conclusion. I can plainly state that sanctioned religions in the Judeo-Christian tradition have no future. These religions have nothing to do with the functioning of a state. They have to do with the individual and the social institutions in which individuals usually operate. The state and its function as a religious supporter is dysfunctional.
Islam, with a focus on the state for tribal societies, doesn't face this problem.
American religions face the serious problem of permanent schismogenesis. They are always splitting into smaller and smaller units and losing their theological cohesion.
All of which leads me to suggest that the religions that will survive are the ones that operate in an open ended environment. Christianity grew as the Eruopean powers expanded their empires and stopped when they stopped. The American expansion helped many religions such as Mormonism. That may be at an end now.
When a religion is faced with a closed system, such as the European nations, they lack vitality. When they are in an expansionist mode as Islam was for many centuries and Protestantism was for a few centuries, they had vitality and experienced growth.
In a world where the competition is not other religions but societies without religion... China, India, Japan and much of Africa, I think we will see a decrease in religion. All religions, including Islam.
Religion also has a problem with commerce. Commerce in the workplace demands tolerance of religious diversity. This tends to make religion a much more superficial status matter and less of an organizational church matter. It becomes an association with ‘a higher power’ as the diverse AA has evolved.
In summary if a religion can confront an expansion of religious opportunity it can remain vital. Religion benefits from converts. When we are in a tribal environment, pre-modern industrial commerce, religion can remain an important structure for maintaining the family and moral behavior. Right now I see no significant religious expansion. I see even less in the rest of this century.
However, as we become more commercial and diversity in the commercial environment becomes more important, religion declines and becomes a superficial phenomenon.
(None of this applies to Jews, for which there is no human survival explanation.)