No, never happen. The people of the world are too diverse.
Will there ever be just one religion?
Not in this system, no.
The bible says that it absolutely will be just one religion. There is only one way to worship God, everything else is man made and unacceptable.
The bible says at John 4:23, 24 -
Nevertheless, the hour is coming, and it is now, when the true worshippers will worship the Father with spirit and truth, for indeed, the Father is looking for ones like these to worship him.+ 24 God is a Spirit,+ and those worshipping him must worship with spirit and truth.
Eph 4:5 "One Lord, one faith, one baptism"
We are not allowed to make up a religion that will suit they we feel. God has a standard that is designed to unite mankind in line with his purpose to fill the earth with humans using their "free will" in line with his purpose. Since everyone is not willing to do that, there must be a way of getting people together to accomplish that purpose. Our wise creator has such a way and it will result in his purpose being realized. An earth filled with humans using their "free will" properly and enjoying the life God purposed for them.
The religion of life.
You are the god you seek.
Come together as one people, and one planet.
No matter how mixed up and scary it all gets,
it can work.
No . There's more than one religion.