Religion isn't going away. Ideology is religion. Very bad religion, but it is religion (or a "cult" to use your language, though that term is overloaded). And no one is without religion. Everyone worships something. The question is: are you worshiping the right thing?
In terms of the "traditional" churches in the US, yes, mainline Protestantism is dying because it is a spent force (it has more or less fully acquiesced to the culture, become a consumer and servant of that culture, which means it no longer has any purpose). Muslims who move her tend to become moderates and likely shed Islam entirely eventually. You do see some growth among Evangelicals, but in any case, globally (Africa, Asia), you do see Catholicism and Islam growing. The West is in this sense a decadent freak.
