I will begin by saying that I am persuaded by most of Derek's claims and arguments. That may tend to make for rather uninteresting commentary, but I shall try to find something to say. I shall offer only one criticism of the main part of Derek's paper, and then I shall discuss at somewhat greater length the questions he raises in the last section of his paper.
In the main body of the paper, Derek attempts to prove that if we accept what he calls the Complex View of personal identity, then we must abandon what he calls the Equal Concern Claim of Classical Prudence. The basic argument is simple. On the Complex View, personal identity is a matter of degree. But it is not irrational to think that a fact which is a matter of degree is of lesser importance when it holds to a lesser degree. Therefore, it is not irrational to think that one's identity with oneself in the distant future may be of lesser importance than one's identity with oneself in the near future. It follows that it is not irrational to give greater weight to one's interests in the near future. Classical Prudence is not a requirement of rationality.
My only criticism of this argument may seem, and indeed may be, niggling. Derek relies on the claim that on the Complex View identity is a matter of degree. But is it, necessarily? The Complex View is defined primarily by contrast to the Simple View. Derek also says that on the Complex View, "the fact of personal identity over time just consists in the holding of certain other facts," such as various kinds of psychological continuity. Now suppose someone says, "Personal identity consists simply in continuity of physical and psychological development nothing else. That is, we look at one person-at-a-time and another person-at-a-different-time; if the person-at-the-later-time developed by a continuous, non-disrupted process from the person-at-the-earliertime, then the two are in fact the same person." I shall call this view the Developmental View. It seems to me that the Developmental View is a Complex View, in Derek's terms, but a Complex View on which personal identity is not a matter of degree.