Are people who never heard the gospel still responsible on the day of judgment?
Yes. Scripture indicates those who never heard the Gospel are still responsible at judgment. The light enlightens every person, God's power is manifest in them, and His grace has appeared to all, leaving them without excuse. They could have known, but did not choose to.
Les explains that these verses can be mind-boggling, but Scripture does not lie. He ties John 1:9—the light that lights every man coming into the world—with Paul's statement that God's power is manifested in them so they are without excuse, and Titus 2:11, where God's grace bringing salvation has appeared to all men. Les then considers people in the jungles of South America who seem never to have heard the Gospel; in light of these verses, they are responsible. They will come before the great white throne lost and without a word of excuse, yet God will be absolutely fair and just. He will be able to say, "You could have known." The only reason they did not know is that they did not choose to. Les admits this is hard to comprehend.
For the grace of God that bringeth salvation hath appeared to all men,
That was the true Light, which lighteth every man that cometh into the world.