I can't help wondering what would have happened if we didn't have the liturgical reforms of the 60s/70s, there is nothing within the Catholic Church to help answer the question except Fr Montgommery-Wright's parish in France and the diocese of Campos in Brazil, where there were no loss in numbers, the working class seem to have remained faithful, both were headed by exceptional and somewhat eccentric clergy.
Perhaps the the Orthodox world might offer a clue, in Greece the decline though not as dramatic as in the Latin West seems to follow the same general decline but in Russia things are quite different. According to a recent Pew Forum survey over 70% of Russians identify as Orthodox. I remember a time when there were cities without a single open Church and Moscow and Leningrad (now St Petersburg) a solitary priest offered the liturgy in almost derelict cold churches for a few elderly women.
One must remember that many of the Russian Church's structures are the same as before the Revolution 100 years ago, they haven't undergone the changes that affected the West. The liturgy is of course unreformed and in Church (or old) Slavonic.
A friend of mine, a Greek bishop, who was recently a guest of the Patriarch of Moscow saw a Church which was quite different, the churches he was taken to were revitalised, full of young men and women on Sunday's and feast days, he visited four of the Moscow seminaries each with between 300 and 400 hundred seminarians. In formerly atheistic Russia there are now chaplains in the military and even in schools. There are huge outdoor processions and services and the number of baptisms increases year after year. Monasteries and convents once derelict are now filled with monks and nuns.
Obviously, Putin has used the Russian Church to construct the narrative of Holy Mother Russia after years of Soviet destruction not only of the economic and social infra-structure of Russia but also of the souls of individual Russians. It is worth remembering that at one time during the Soviet era women had an average of seven abortions in their life time, leaving Russia under populated.
I often wonder if Our Lady has appeared to young shepherd somewhere in Russia and has asked for the Consecration of, and prayers for the Conversion of the West. Perhaps when we realise that the West is in a similar situation to the Soviet Union in the 1980s our political leaders might realise the rediscovery of Christian Europe could offer it a form of moral regeneration, unless of course they turn to Islam.