Not certain what you are attending, but the Romans passage states that the heathen are responsible because of the evidences written even on their hearts.
Are you concerned about "these Amazons, for instance, who hunt birds with poisoned arrows, and have scant ties with civilization, will be judged" and their eternity?
You seemed to be saying that the Decalogue (in its entirety, I assume) applies to the heathen. That assumes their needing to observe the Jewish Sabbath.
My point is that Sabbath observance is a non-moral law. It was purely didactic and prophetic. And for the Jews only.
Certainly the heathen cannot be faulted for non-observance of a law that has nothing to do with them. (I am not speaking of the other nine. Clearly these all have universal application beyond the Judeo-Christian world.)