For another purpose, I recently collated the most reliable statistics on religion from around the world: it turns out that about 10% of the world's population do not practice a religion. It would seem that reports of the death of religion have been somewhat exaggerated.
Having one's name 'on the books', so to speak, does Not necessarily make a person belonging to a religion as being religious.
There is nothing in the Bible showing that religion ( even if in name only ) will have a slow demise or decline.
Rather, the world's religions ( the composite religious queen of Rev. 18:7 ) thinks she sits as some sort of religious queen that will never see mourning or sorrow or demise.
According to Scripture, house cleaning starts with the House of God with the so-called Christians ' in name only ' - 1st Peter 4:17.
Jesus comes as a thief - 1st Thess. 5:2,3 - that of course would mean comes by: surprise!
So, the religious organizations of the world will Not expect any divine involvement, and will be surprised when suddenly - Rev; 18:7-9,19 - the spiritually dried-up religious ' waters ' ( her people - Rev. 17:1 B, 15; Isaiah 57:20 ) will be of no help.
So, religion will Not just fade or die away. Religion will try to remain a potent force on the world's scene in attempting to bend the political rulers (kings) to do her will until that surprising day when the political will turn on the world's religious groups.