One thing is that you just won't know, as you won't know what was in this relative's heart at the hour of his/her death.
The Lord promised great mercy to all who call upon His name, as reported her from a dialogue with St. Faustina:
Our Lord said to the servant of God, Sr. Faustina: "Unceasingly recite this chaplet that I have taught you. Whover will recite it will receive great mercy at the hour of death ... Priests will recommend it to sinners as a last hope of salvation. Even the most hardened sinner, if he recites this chaplet even once, will receive grace from my infinite mercy. Oh, what graces I will grant souls who will recite this chaplet... By means of it you can ask and obtain anything if what you ask will be compatible with my will.... I want the whole world to know my infinite mercy. I want to give unimaginable graces to those who trust in my mercy...
So hope is not lost...