Although the Bible does not give us the complete answer to this question, it does tell us that God “will judge the world in righteousness and the peoples with equity (or fairness)” (Psalm 98:9). God will not condemn a person for rejecting a Christ they never heard about. However, we already stand condemned for something far more basic.
God has revealed Himself to everyone through the creation around us and the sense of right and wrong inside us. Each person knows enough about God that He says we are “without excuse” (Romans 1:20). It is for this suppression, distortion and rejection of the true knowledge of God and for the accompanying violation of God’s laws that we stand condemned.
Only by casting oneself completely on the mercy of God, and not counting on any of one’s deeds — religious or otherwise — for right standing with God, can anyone possibly be saved.