The mainline churches are in critical condition. In 50 years or less, they will either cease to exist or have consolidated into one "United Church" style organization.
I remember reading a statistic in the early 1990s claiming that the probability of a person raised in the Presbyterian Church (USA) staying in that denomination in adulthood was below 25%. Those who move toward a more Biblical position will probably head toward an evangelical denomination, Calvinist or not.
Count me as one of the 75%. When we moved to this town in the early '90s, we visited various churches. At First Pres (PCUSA, naturally) the pastor lead the Lord's Prayer as "Our Father and Mother,. . ."
Needless to say, we didn't go back. We started going to the local Evangelical Free Church (which I guess could be classified as generic evangelical), and have been members there for 5+ years at this point.