written out of the book of life,

No one is written out of the book of life. No one’s name is written in there until they are saved.

Paul already explained the case of those who don’t know God’s Word in Romans 2:12-16. Though they don’t have God’s Law, they have their own laws and conscience that show that they are sinners as well.

Furthermore, I have heard multiple reports from Muslims in the Middle East who live in countries that heavily suppress the gospel. They say that no man came and preached to them, but that Jesus appeared to them in a vision and shared the gospel. It seems that many Muslims in this situation get saved this way; God has a way of getting the gospel to those who are isolated from preachers or missionaries.

Lastly, there is evidence that nearly every ancient culture, even those that predate the Israelites, had some knowledge of the gospel, and this knowledge was encoded in the names of the stars and constellations in the zodiac.

https://barrysetterfield.org/stargospel.html