I believe that the most Christian stance is to remain agnostic on this question.  When somebody asked Jesus, “Lord, are only a few people going to be saved?”, he refused to answer and instead urged them “to enter through the narrow door”.  The fact is that God, alongside the most solemn warnings about our responsibility to respond to the gospel, has not revealed how he will deal with those who have never heard it.  We have to leave them in the hands of the God of infinite mercy and justice, who manifested these qualities most fully in the cross.  Abraham’s question, “will not the Judge of all the earth do right?” (Gen 18:25) is our confidence too.