Europe will shift from Christianity to Agnosticism to Islam. China from Atheism to Christianity and Islam. Americas will slowly go agnostic and then may be buddhist/hindu/muslim/non-organised etc. Muslim regions will remain muslim. There isnt gonna be any standoff between Islam, Europe and China. As American superpowerdom fades away, the wars between east and west will also fade. Eurasia will start to merge slowly with cross pollination of religious ideas. Just recently Putin has opened a huge mosque (10000 worshipers) in moscow, and dubai sheiks started a hindu temple.
China will slowly rule the world. IMO there might be problems between Christianity/Islam and Government/religion in china. They'll deal with it their "regular" way for sometime.