Correct [the boy killed by a Christian drunk driver goes to hell, while the latter goes to heaven]. However, you seem to forget that God is the One Who determines when a person will die, and if He allowed the young boy to die in that state, the implication is that he never would have changed in heart anyway. The man, though sinning by driving dangerously, is still saved for eternity, since in his heart he is willing to accept Jesus' offer of salvation. He does lose some rewards, though. Again, justice and mercy are maintained.