Hello there...
For the start, what is your goal of the whole thing, here? Just to see other people opinion? It all started as question on religion, but ended as expected: The First Question Ever Made?!
There won't be any answer if God exist or doesn't. Never.! But that later...
The concept: belief is different from religion. Every human being believes in something (he believes God(s) exist; he believes that God(s)does not exist). So, belief is not connected to religion. Religion only uses it. Religion has other principles than beliefs. Religion has more political background than spiritual. As Napoleon said, "Religion is the only thing that the poor does not kill the rich". That is why Kings/Emperors and other rulers chose there religions and tried conquer more lands. It was a used as a weapon in order to control people and lands. You just have to get a normal history book and see the patterns that happened in the Roman Empire, later in the Holy Empire and the 16th cc. In those eras there were the biggest religion fights. It all was made to make people follow them as sheep, to have fear, because there is something that watches you over and sees everything, after his judgment you may go to heaven or hell.! Bad=Hell; Good=Heaven. In Islam even they gave you virgins. (They just didn't specify what kind of virgins.!)
Humans have ever believed in something. There is no man, woman, child that does not believe in something. (I actually want to believe in Santa.. At least i get presents even if i am not an angel.) So, people will continue to believe in something and will share there experience with others, so organized (syn.organised) religion.
About God or gods. Well, Imanuel Kant once wrote that, in this life we won't experience God, even if it exist, because he is beyond our capability to perceive Him. That might actually be true, but what or who is God? Is it really a wise-old-man that lives on top of a cloud? That's the whole point of the farce.. Every man has his own view what He is. That makes Him individual and specified to your needs. In reality, you create God not he creates you. The funny thing is that He gets all the merit of creating...
Answering to the question before all this. Will religion decay or disappear? Probably not. If the mission of religion is completed than there is no longer point to exist, so... Religion has far-going missions and that means it may mutate, but not disappear. It's too economical for some to be let buried.
For a fact, how many believers are in the world that believe to a God or gods? In the world are round about 6,6 billion people.. Christianity "control" some third of it. Imagine.!