It has happened often in the vast history of the Church that the numbers of the faithful have dwindled in the face of heresy and unfaithfulness. Recall that the Arian heresy, which lasted from the 4th to the 7th century, at one time claimed up to two-thirds of all bishops before finally dying out, and the Church finally regained it’s orthodoxy and numbers. Similarly, when droves of people followed ther political leaders into Protestantism after the “Reformation,” the Blessed Virgin Mary, as Our Lady of Guadelupe, came to the Americas and preciptated the conversion of millions, effectively replacing in number the apostates that had been led astray.
I can’t presume to speak for your particular ecclesial non-Catholic faith community, but secular and Protestant publications that I’ve read point out the growing number of Protestants (especially evangelicals) that are headed for the huge mega-churches where style triumphs over substance and show over content, giving people feel-good easy-believism. As this trend continues, smaller ecclesial non-Catholic faith communities are dying out along with the historic Reformation-era bodies (though of course more denominations are always popping up – seven a week by some tallies). I personally see this trend as one of the death-knells for serious Evangelical Protestantism.
Meanwhile the Catholic Church rolls on and on, just as Jesus said it would (Matthew 16:18)…