There is no pardon for a person who dies in his rejection of Christ. The Holy Spirit is at work in the world, convicting the unsaved of sin, righteousness, and judgment (John 16:8). If a person resists that conviction and remains unrepentant, then he is choosing hell over heaven. “Without faith it is impossible to please God” (Hebrews 11:6), and the object of faith is Jesus (Acts 16:31). There is no forgiveness for someone who dies without faith in Christ.
God has provided for our salvation in His Son (John 3:16). Forgiveness is found exclusively in Jesus (John 14:6). To reject the only Savior is to be left with no means of salvation; to reject the only pardon is, obviously, unpardonable.
So if the unrepentant sinner remains in that hardened condition till death, he or she has committed the unpardonable sin since they have rejected the only pardon there is.
Final impenitence.