Wouldn't matter OTWO, as evidenced by some of the comments above.
These people who today swear that 'god created heaven and earth', if transported back into time and observed that god had nothing to do with any of it, would simple create 'talking points' that allowed evolution and non-god in our past evolutionary history, while still claiming god did it to 'show he could' or whatever invented defense they would have after the experience.
Religion is morphing now. Scientific evidence that disproved the Garden, Adam, creative days, the flood, etc, are all just changed to allegorical or excused away in some other fashion. If they went back and observed that Moses did not encounter a burning bush, or that Ararat was just a smoking volcano, or that the Red Sea never actually parted, or saw that Jesus' miracles never happened, it still would not matter to them.
They want to believe in god due to fear of eternal death. They just don't know that is the reason. Man has always had gods for this very reason. Because they don't believe that they should die, that they are mortal like the animals. Surely god is up there preparing a heavenly home for them. They are special, guided by angels, protected by jesus, and soon going home to a place they have never been.
Fantasy is getting harder to defend though. Religion will decline in the face of massive evidence that shows the Bible and other holy writ as a collection of myth and fairy-tales. But it will not go away. Too bad.
Jeff