@thecronosone It's not so simple as that to assign motives to the father. People in general will chat on friendly terms with the taxi driver, barber, what have you. That same relationship does not necessarily support asking for a favor from someone who previously heard you were abusive. The question might seem completely unapproachable if you happen to be a recovering, guilt-stricken man.
The story establishes "recovering" pretty solidly. "Guilt-stricken," and thus (perhaps) forgiveable, is left for Don to discover, and that's kind of the point. Whether he likes it or not, Don holds on to sentiments good and bad, and he owes it to himself to resolve things. He comes back to town to see Elizabeth off, but it's not a proper resolution. Over her grave, he's full of things he never got to say. Liz's daughter stands in contrast, having said goodbye many times at the hospital. Her mother's death represents a far more central loss in her life than Don's, but Don would have given an arm and a leg for the precious chance she had; to set things as straight as possible while there was still time.
For you, it suffices to surmise, perhaps correctly, that the father's actions demonstrate that he is a lost cause, worth no further thought nor attention. Don discovers that for him, it does not suffice, and that he would rather understand his father for certain than burden the rest of his life shutting away the insistent hope that asks "what if?". No doubt he's taking a risk. But he's a man now, with gained experience and strength of character. He can handle taking upon himself the two things that are coming, and it's not an either/or.
Perhaps he reopens old wounds. That merely affirms their purpose.
Perhaps healing is possible. Well, wouldn't that be nice?