Is it obligatory to fast for two months for someone who unintentionally killed a person in a car accident, knowing that the deceased intentionally threw himself in front of the car and intended to commit suicide?

If a person causes the death of another, and the deceased could have saved himself but did not, instead pursuing the cause until he perished, then his blood is considered forfeit (damuhu hadar), and no blood money (diyah) or expiation (kaffarah) is due from the one who caused it, because he destroyed himself. Scholars have analogized this to someone who is thrown into water and is capable of swimming but abandons it until he dies; his blood is considered forfeit. The situation mentioned in the question is even more deserving of the blood being considered forfeit.