For various reasons that I won’t go into here, I find the Nephi-killing-Laban episode to be the most striking story from the Book of Mormon. If it is read as a retrospective account, it seems that Nephi or some later hand has crafted the story to certify that the killing wasn’t cold-blooded murder but an inspired killing that is beneficial both to Nephi and countless others. In Nephi’s internal dialogue about whether or not to kill Laban, it is the divine permission/command that tips the balance in favor of killing even though Nephi offers some well considered reasons to the contrary. Scary stuff.
Lately I have been immersing myself in the issue of Stoic suicide and I have been blazing through various Stoic thinkers who treat of suicide. Two of the big names in this area are Epictetus (who now has a canonized dictum in the Mormon scriptural corpus thanks to a shout out by President Monson at the last General Conference) and Seneca. Epictetus was a freed slave who became a famed Stoic teacher some of whose words survive through the efforts of a devoted student (Epictetus was born mid first century, died probably in the 130s). Seneca was the personal tutor and confidant of Nero many of whose moral writings survive as well as some of his Latin versions of Greek tragedies (Seneca was forced to commit suicide by Nero in 65, a common fate for many elite Roman men in that year).
Seneca is famous for his obsession with suicide. In his moral essays and epistles he lauds and romanticizes suicide not just as an option for the Stoic philosopher (for Stoicism did allow for suicide as a virtuous exit from life) but he more than once suggests that it is the mark of a true Stoic. His hero, of course, was the Stoic Cato (the Younger) who disemboweled himself at Utica rather than surrender to Caesar. But Seneca was not advertising suicide for the masses. No, he revered the act too much for such vulgarity. Only those with sound reasoning were justified in killing themselves. For Seneca reason (ratio) was the deciding factor in the calculus of autothanasia.
So in my vastly over simplified discussion there is well-reasoned Stoic suicide proffered by Seneca and there is divinely appointed Stoic suicide taught by Epictetus. Reason. Divine inspiration. Killing. Based upon the Nephi-killing-Laban narrative as we have it, if Nephi were to consider suicide it seems that he would probably be an Epictetus man and err on the side of divine inspiration after a bit of reasoning. If conditions were to come down to it, which suits you? As much as I really like the idea of a divinely inspired, self inflicted exit from life (so much comfort and assurance!), I have to think that I would be a Seneca man and let reason carry the day.
You may also want to ask yourself WDJD (What Did Joseph Do)?