All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His Slave and Messenger.
Deciding that a specific person will enter Paradise or Hell is based mainly on what is mentioned in the Noble Quran and the honorable Sunnah. However, we hope the good person will be rewarded and fear that evil may afflict the bad one. Then, we can say that those Muslims who observe the obligatory prayers regularly will enter Paradise as long as they die on Islam. If anyone of them entered Hell due to some evil deeds, then he would not remain in it forever for the Prophet, sallallaahu ‘alayhi wa sallam, said in: “Allaah The Almighty Says, ‘Bring out (of Hell) whoever has a seed's weight of faith in his heart.’” [Al-Bukhari and Muslim]
So, Ahlus-Sunnah Wal-Jamaa‘ah do not deem anyone of the Muslims in the broad sense as a disbeliever, regardless of the sin he committed except if he considered such a sin lawful or if it was an act of Shirk.
However, deciding that one of the Muslims in the broad sense will enter Paradise or Hell mainly depends on what is mentioned in the Noble Quran and the honorable Sunnah of the Prophet, sallallaahu ‘alayhi wa sallam, such as the ten Companions who were given the glad tidings of entering Paradise while being alive, ‘Ukkaashah ibn Mihsan and the like. Practically, good reasoning has nothing to do with this issue.
Also, we would like to draw your attention to the fact that the one who repents of a sin is like the one who has no sin. There are many texts of the Noble Quran and the honorable Sunnah of the Prophet, sallallaahu ‘alayhi wa sallam, proving that the repentance that meets all its known conditions will purify the sinful from all sins. The most clear-cut evidence is the Saying of Allaah The Almighty (which means): {Say, "O My servants who have transgressed against themselves [by sinning], do not despair of the Mercy of Allaah. Indeed, Allaah Forgives all sins. Indeed, it is He Who Is The Forgiving, The Merciful.}[Quran 39:53]
Moreover, It was narrated on the authority of Abu Moosa that the Prophet, sallallaahu ‘alayhi wa sallam, said: “Allaah Stretches forth His Hand at night to Accept the repentance of the one who sinned during the day, and He Stretches forth His Hand by day to Accept the repentance of the one who sinned during the night, (and that will continue) until the sun rises from the west.” [Muslim]
Not crying after the words of the American woman is because you are pleased with her words, and the souls always love glad tidings. We believe that her words are just a kind of expressing condolence in her society. Our advice is to ask Allaah for forgiveness for your father frequently. Furthermore, you have to be dutiful to him after his death.
Allaah Knows best.