so I predict it will start dying out some time around 2020-2200
That's a really rather specific estimate for it.
Especially to suggest it might start dying in just five years time.
Christianity as a whole (including Catholocism and the various Protestant sects) is the worlds largest religion, being approx. 2.4 billion people, or around 33% of the global population.
And it's still growing, both in being spread to more people, but also just because the global population is increasing, particularly in areas where Christianity is gaining numbers or is already massive, such as South America, Africa and Asia.
Just given the fact that most Christian families have Christian children, I think you'll be guaranteed that Christianity will continue as a major religion for several centuries, if not a millennia or two.