When Popova writes
But then, when that day loomed near as he grew old and infirm, “the poet of the body and the poet of the soul” suddenly could not fathom the total disbanding of his atomic selfhood, suddenly came to “laugh at what you call dissolution.”
I think she is saying he laughed because he realized something about the whole of who/what we are. Following soon after the stanza in Leaves of Grass about our sharing all our atoms he writes
My tongue, every atom of my blood, form’d from this soil, this air,
Born here of parents born here from parents the same, and their parents the same,
The way I read it he doesn’t so much reject death and with it life as he comes to see it as a whole stretching back through ancestors and on through progeny and through every sort of creature forever. There is no where to go. Day, night. Life, death. The world and our place in it goes on, only that which most sets us apart one from the other comes to an end. If we identify only with these eyes, these finger prints and the biographical features of this lifetime, then indeed we go into oblivion when we die. But I think he realized we are the world and have no where else to go … or somthing like that.