Question: Was there any explanation given for D'Leh's father leaving his home and tribe so suddenly?
Question: What happen to D'leh's dad?
Answer: When the mammoth numbers diminished, D'leh's father (the chieftain) left on a quest to find new hunting grounds in order to feed the tribe. Not knowing the true nature of his quest, many tribesmen thought the chieftain left because he was a coward, which was a source of anxiety and guilt for D'leh. Later in the movie, it is learned that D'leh's father was captured by slavers and died as a slave.
Charles Austin Miller
Answer: It is explained that he decided not to wait for the last hunt and left to find another way to feed the tribe. He left in secret so that others would not follow him abandoning the tribe.