Salvation for Protestants who knowingly reject Catholicism?

Father John O'Brien wrote in The Faith of Millions

... those who are convinced of the truth of the Catholic Church, but who for some selfish reason fail to profess their faith in her. It is only these ... who remain out of the Church, in bad faith, until death, that the Church teaches that the words of Christ apply: "He that believeth not, shall be damned."

I certainly hope you don't fall into that hole. I have some dead uncles who I hope didn't fall into that hole too! That kind of obstinancy requires hard work and determination (or willful ignorance). Fr. O'Brien goes on to write:

it is the view of the Church that every person who, with an open mind and without prejudice investigates in a careful and impartial manner, the evidence of her claims to be the one true Church can scarcely fail to be convinced of the truth of those claims.

So, one would hope it is a learning process. Few are convinced overnight. If you read Orthodoxy, by G.K. Chesterton, you'll have read the auto-biography of a man who was utterly convinced, but remained outside the Catholic Church for another 12 years. He found the truths in the Catholic Church to be astonishing. He admired it because it is a "Truth telling thing". Everyone, with a soul, applauds whem seeing truth spoken to power; but it makes power nervous. When truth is spoken to everyone, everyone gets nervous - it's a natural consequence of our fallen nature. Chesterton has no more "Idea of becoming a Catholic than becoming a Cannibal"

Fr. O'Brien goes on to say that the reasons for not being convinced may stem from antagonism or prejudice taught in ones youth or some otger subjective circumstances. Not that these are good things, but they're not salvation inhibitors. Still Catholics would like to win you to 'their side' so that you can participate in the sacraments, which they find to be "sure signs of salvation". Namely, the Eucharist and Confession.

The last thing to consider is what you actually do beleive. Where did your morality come from. Was the culmination of all of history with or without the Catholic Church? Was it riding the momentum of the Church until the split and now it is coasting on it's own? Does it progess? Does it have answers to the new attacks on religion? Does it preseve the old truths? Fr. O'Brien claims that protestants and irreligious people are actually borrowing from that which has it's roots only in Catholicism today. Basically, and arboralleally, you can't plant a sucker in the ground and expect an apple tree, you can only really graft it to another tree that has already got some roots.

So, the Catholic Church would exist with 0 living members and people would still be saved after death through the Grace of God. So I think you need to re-evaluate what is meant by necessary. I doubt many people come to believe because the existence of the Church equals x in their faith equation x + Jesus = saved. People believe what the Church teaches because it reveals Jesus in a way we couldn't do on our own. Pope Paul VI also showed in humanae vitae that the Church is the interpreter of the natural moral law. Both of these things, a close relationship with Jesus and clear discernment of right and wrong, can sometimes be acheived sans-ecclesia, even perfect contrition can be attained without confession (says Fr. O'Brien). But these things are made much easier with the spiritual grease that is Actual Grace which the Catholic Church spreads out on a table for you to partake of every day.

Pope Benedict XVI said, in an ecumenical dialouge at the Cologne World Youth Day that our divisions are "contrary to the will of Jesus" and he went on to make pathways to full communion for some sects. Pope Francis is continuing that and speaks openly about ceasing divisions with the Orthodox Church.