Fifty years from now, worldwide secularization will be much more dominant than it is now. Worldwide leftists will continue to criticize Christianity and suppress Christianity much worse than they do now. Worldwide Islam will be much more common. Worldwide Christians will be forced to practice their faith in secret.
I have no inside information, but I would not be surprised to see a country wide/world wide fundamental Christian revival. The true word of God will prevail.
On the path we are currently on, this part of your statement is probably true. Then again, one giant worldwide depression or something like it could completely change the direction the world is going in. But yeah, I think Western Christianity is likely to continue weakening as populations in the Western world secularize.