This can be thought of as a different type of memento mori and a much more pleasant way to consider death than some Eastern methods, in particular the contemplation of the body in various stages of decay. Further, we have textual evidence that Epicurus went through this exercise, although that evidence doesn’t provide particular context as I recall.
Writing a will isn’t a one-and-done thing: it should be periodically updated as one’s circumstances change. And it may involve the more elaborate exercise of putting together or revising an estate plan, depending on one’s circumstances.
There’s more to this than just thinking about one’s demise. It can also extend, say, to the consideration of the categories of desire. What is natural and necessary, natural and unnecessary, and/or unnatural when thinking about one’s length and quality of life? All three categories come into play, and in contemplating this one can also gain a greater appreciation and understanding of the three categories and how they many apply to one’s life. For instance, to what lengths would one go to improve one’s health or to prolong one’s life? At what point might doing so involve an inordinate amount of mental and/or physical distress, and at what point might this distress interfere with one’s well-being?
Since this exercise, by its nature, involves thinking about spouses, children, and what may remain when one is no more, it also touches on the controversy as to whether or not Epicurus espoused (as it were) marriage and having children. The textual evidence isn’t clear but, as with all things, one must apply the philosophy to one’s own life in order to get a fuller understanding of it and to make it useful. Knowing that at some point either one’s spouse or oneself is going to die, how do the categories of desire apply to that knowledge? Likewise, knowing that one can only be as happy as one’s unhappiest child, and that one only has limited control over such happiness, how do the categories of desire apply?
Or consider the Stoic treatment of what’s in one’s control or not in one’s control. Is that similar to what is being thought about in this exercise? What is the end result of each approach? Which brings the most complete happiness?
For reference:
PD21. One who perceives the limits of life knows how easy it is to expel the pain produced by a lack of something and to make one's entire life complete; so that there is no need for the things that are achieved through struggle. [Peter St-Andre note: The word ἀγών, translated here as "struggle", originally referred to the contests pursued by athletes at public festivals such as the Olympic games; Epicurus is not necessarily counselling against personal discipline (such as that involved in learning true philosophy), but against the trials and dangers of action in the public arena.]
PD29. Among desires, some are natural and necessary, some are natural and unnecessary, and some are unnatural and unnecessary (arising instead from groundless opinion).
PD26. The desires that do not bring pain when they go unfulfilled are not necessary; indeed they are easy to reject if they are hard to achieve or if they seem to produce harm.
PD30. Among natural desires, those that do not bring pain when unfulfilled and that require intense exertion arise from groundless opinion; and such desires fail to be stamped out not by nature but because of the groundless opinions of humankind.
LM127-128 ...keep in mind that some desires are natural whereas others are groundless; that among the natural desires some are natural and necessary whereas others are merely natural; and that among the necessary desires some are necessary for happiness, some for physical health, and some for life itself. The steady contemplation of these facts enables you to understand everything that you accept or reject in terms of the health of the body and the serenity of the soul — since that is the goal of a completely happy life.
Here I’ve just been thinking about this in terms of the categories of desire, but the subject obviously doesn’t stop there! For starters, much more of the Letter to Menoikeus applies, as do other PDs.