Q: What happens to those who have never heard the gospel? Are they sent to hell because they didn't accept a Jesus Christ they never heard about?
A: Men and women are not sentenced to hell based upon whether or not they have heard of Jesus Christ. Rather, they are justly and fittingly condemned based upon the fact that they are sinners. Indeed, they are sinners who have failed to act responsibly on what God has already revealed to them -- whether through the light of creation (Rom. 1), through the light of conscience (Rom. 2), or through the light of Christ (Rom. 3). If people respond to whatever light they do have, then God will send them the light of the gospel. Because no one has been kept in the dark about God's existence, we're all accountable directly to Him (Luke 12:47-48).
While the Bible affirms that Christ is the only Savior (Acts 4:12), it also states that God is truly just (Job 34:12) and that He loves humanity with an everlasting love (John 3:16). Let us, therefore, labor all the more to bring God's message of reconciliation to a world in desperate need of salvation (Rom. 10:13-15), knowing that there is no other way to reach Him except through His Son -- the Lord Jesus Christ (John 14:6).
Finally, we should ask, if those who have never heard the gospel are indeed bound for heaven, why should we attempt to evangelize them? Wouldn't it be more prudent to just keep everyone in the dark? In fact, if you really draw this argument out to its logical conclusion, Jesus Christ would not have come to seek and save those who are lost, but to seek and lose those who are already saved! He would then not be the great Savior of the world; He would become its great destroyer.