Christ let Peter's denial go unanswered for a period of time, denying him an immediate restoration of relationship; and then rather, Jesus sought out Peter that he may be restored. Jesus rebuked him publically among several of the disciples, as was fitting for his public denial of Christ.
Peter was grieved in the heart at what he did, knowing his profession of faith and his believing in Christ. Should he have died in that state of denial, he still believed into Christ, and had eternal life in Him. The point is not what might happen if we die physically, but what God does with believers because we are alive in Christ. He desires to teach us His ways. Should we not walk in them, or should we rebel even from the heart, it is God's desire to correct us and to restore us. We stand in His grace, and we belong to Christ having been set firmly in Him, and we are sealed by His Spirit.