Does the foul odor emanating from a dying patient, despite their commitment to acts of worship, indicate a bad end, or is it due to chemotherapy and lung deterioration?

Praise be to Allah for His grace upon your father, that he returned to prayer before his death. His mention of being in a state of impurity does not justify abandoning prayer; rather, it was obligatory for him to purify himself and pray. If he was unable to purify himself, he should have prayed in his existing condition. As for the emission of an odor from him days before his death, we have no knowledge of this matter; it should be inquired about from medical professionals. It is important to note that the emission of this odor does not constitute evidence of a bad end for your father.