Even as all men die, the same all will be made alive through Christ (I Corinthians 15:22). Everyone who has ever lived and died will be resurrected—first Christ was resurrected, then later the saints who lived before Christ's Second Coming will be resurrected at His return.
But what about the vast majority who were not Christ's? Paul in I Corinthians 15:24 includes them all in "the end"—when Christ completes His job of conquering every enemy (verse 25). That will happen after the Millennium (Revelation 20:7-10).
Those who have not heard or understood God's truth have not been irrevocably condemned to eternal death. They have not sinned willfully. They have not had a chance! Even if they lived up to the best they knew while alive, the Bible teaches that there is only one way to salvation—through belief in Christ and spiritual conversion and growth as defined in the Bible.
Most of our loved ones who have died "unsaved" did not die eternally lost. They most likely were not called during this age, but their call will come later. After the Millennium they will be resurrected to mortal life and given spiritual understanding and the opportunity to become members of God's Family.