The 2015 Pew Research Poll of US Catholics reports that 40% of Catholics have left the Church and not returned. http://www.pewresearch.org/fact-tank/2015/09/15/half-of-u-s-adults-raised-catholic-have-left-the-church-at-some-point/
"There has been speculation that the popularity of Pope Francis and the atmosphere of change around his 2-year-old papacy might inspire many former Catholics to return to the church. But when it comes to ex-Catholics, Francis has his work cut out for him. Only 8% say returning to the church is something they could imagine doing."