What should I do to honor my deceased father after feeling I fell short concerning him? And is he considered a martyr and among the people of Paradise due to his suffering from illness, his patience, and his death from an abdominal ailment, even though he was a smoker?

May Allah magnify your reward concerning your father, and we ask Allah to forgive him and have mercy on him. We have explained in previous fatwas how a Muslim can honor their parents after death; please refer to Fatwa No. 35111. We hope that your father is a martyr, falling under the saying of the Prophet, peace and blessings be upon him: "And the one who dies of an abdominal disease is a martyr." We have clarified the sayings of scholars regarding the interpretation of "the one who dies of an abdominal disease" in Fatwa No. 49249; please refer to it.

And Allah knows best.