I believe over time the different religions and Governments will all start to slowly meld together, it is far more likely to happen in the long run then for opposing idelogys to continue to hang around and cause conflict, I believe it will be a good thing in the end because there will be more agreement in the world.
Yes syncretism is inevitable. As time goes on religions and schools of thought adapt to new ages. As they adapt they slowly change to adapt to new technologies and current events. This melting pot effect may not take place overnight but it is a slow process that happens over decades.
As the people of our world continue to emigrate, they take with them their beliefs and customs. When their new home assimilates them, and time passes, the host country and the immigrants have tended to fuse many of their beliefs and traditions, thus syncretism occurs. As our world becomes ever smaller, and ethnic divisions blur, syncretism is inevitable.
I do not believe syncretism is inevitable. I think it is wrong to assume that all world religions will eventually fall in together. With all of the wars and fighting and increased sects breaking off from all of these religions I would think people would realize that melding them together is impossible.
I think that there is no reason to believe that syncretism is inevitable. I do think that there will be people who choose to combine some religious beliefs together and be in harmony about such an idea. But I still think most people will still believe in their own particular religion.