There will be little resistance to religion later on. The white walkers and their wights will reduce Westeros to tiny tribes and villages. The survivors of the Ice Age will be few. Each will have its own way of worshipping. Daenerys may not even bring R'hllor to Westeros. She uses religion as a tool. She will do what she needs to accomplish the task of building an empire.
The large lake near Vase Dothrak called Womb of the World is the Sumer in Essos. It is another of the forgotten geographical location of the great empire of the dawn. It is charming to think about. Civilizations rose and developed their own gods. Those gods of fallen cities are brought back to the Mother of Mountains where it all began. Intelligent life did not begin and evolve in one place.