Apparently you did not read the rest of my examples regarding your premise that it can be done without Catholicism or Protestantism. If there is a bible on that island, it has in its translation and compilation of books a clear prism through which Catholicism and Protestantism have left their marks. If you take away the bible being found and replace it with a say an angelic vision, then only in such instances could we say it is without a mark of Catholicism or Protestantism. But are visions reliable without some evidence of conformity to truth?"Premise one is that the "saved survivor" receives reconciliation with God. True." Then you say, "This applies to all Christians, Catholic or Protestant. Your premise #2 is that such a person has done this without Catholicism or Protestantism. At this conjuncture, I disagree with you completely." In other words, you say you agree with this man's reconciliation to God, but then you immediately deny that his reconciliation is valid outside of your formula. You logic is not from God, it is a fleshly logic. It is of no value to you or those who read it.
(addition follows) I mean after all, that the bible's greatest mark is how God over the milliniums of history with mankind reveals a longstanding relationship of truth. A person with only one vision like Muhammed or Joseph Smith has no means to demonstrate with prior revelation the consistency necessary to call their visions accurate, especially when they contradict prior revelation. The man on the island with such a vision would also face the similiar consequences. It would be better for him to not have a vision at all and see God through his creation as Romans 1 would indicate rather than having to find no way in which to test the vision as coming from the Holy Spirit or not.