It is a mistake to say they were saved by their ignorance. Rather they were saved by the truth that God plants on all men’s souls and the truth that he gives them the grace to understand. They are simply not culpable for what they are ignornant of.
13] For it is not the hearers of the law who are righteous before God, but the doers of the law who will be justified.
14] When Gentiles who have not the law do by nature what the law requires, they are a law to themselves, even though they do not have the law.
15] They show that what the law requires is written on their hearts, while their conscience also bears witness and their conflicting thoughts accuse or perhaps excuse them
16] on that day when, according to my gospel, God judges the secrets of men by Christ Jesus.
The Bible gives us many “windows” in to the answer to this question. The Apostles want Jesus to cast fire down upon a man casting out demons in Jesus name. The man is not one of them. Yet Jesus said “those who are not against us are for us” and recommended leniency. The three wise men were not Jews or Christians, yet had some knowledge of God. God’s spirit led them. The Good Samaritan was held up as an exmaple of proper Christian spirit, even though the Samaritans were pagans who included the God of Israel in their many Gods. Cornelius was neither Jew nor Christian, yet was said to be a “God-fearing and righteous man” BEFORE Peter came to him. I don’t believe the God-fearing and righteous go to hell.
With regard to ignorance, it should be noted that in Luke 12 Jesus says “to the one who knew, he will be treated with the unbelievers, but to the one who did not know, he will recieve but few lashes.”. Luke 12 around v. 48.
I have some quotes that I will post later. One from Pius IX.