I have thought about this several times, and am glad you brought the subject up. In order to have an absolute "one religion" do you feel that every one would have to share the same concepts of God, Gods, Satan, Heavan, Hell, Buda, Ganesha, Odin, ect. to be concisdered a religion? Or would it be that everyone could have their own beliefs, talk to each other without bias, and learn from each other? I honestly believe that every religion (or ehat some consider themselves to only having beliefs) hold truth. Devistation would bring people to an absolute reality that we are in need of each other and that beliefs should not set the stands to how we treat one another, but by just watching the news and listening to people talk, this is lost in day to day life. If you really what to know the answer to something, do you not look in every possible place in which that answer may lie? I do not understand why some people find one page that has a fraction to that answer and decide that is good enough.
Sorry for "rambleing". In short, I think it would lead to a unified way of survival, possibly ebbing into realm of religion, but doubtful.