Christ is still alive, in heaven and interceding for us, so if this fellow has true saving faith, his sins are forgiven. All of them. I think the verse in question refers to a lifetime of denying Christ's ministry: the forgiveness of sins through his death and resurrection. It's clear that this fellow didn't lie because he wanted to lead a life of sin, or to bring Christ's name in disrepute.
Having said that, the better decision would have been to proclaim his Christian faith. But if he is truly saved, his sins will be forgiven and his place in eternity is secure. Peter, after all, denied the Lord three times. But he returned and received forgiveness.
For what purpose would he do that? Keep in mind that both God and satan know what is in his heart. Would satan's vicious clowns be swayed? Would the anyone else even know it took place? This is not open court and the rest of those present are dead.