Christianity has always been a generation away from extinction, since the day Jesus ascended into heaven.
But ask Nero, Domitian, Diocletian, Julian ... Lenin, Stalin, Mao ... and many more how well their crusades against Christianity worked out.
I prefer working on/with the current and next couple of generations to worrying about these folks' simplistic statistics. What they see as a trend may be little more than nominal pew-warmers who have always been around being honest to themselves and others.