how has Vonnegut addressed death with using irony and the constant motif, "so it goes'?

In Slaughterhouse-Five, Vonnegut seemingly confronts the subject of death with passivity and nonchalance. Because Vonnegut himself appears in the novel and centralizes Billy Pilgrim's story around an event that Vonnegut lived through, the fire-bombing of Dresden, the novel is seen as his response to World War II and the events that he witnessed, including violence and many deaths.
The catchphrase "so it goes" is the response to any death in the novel, from the death of a fly to the deaths of many humans to the destruction of the universe. It is also the motto of the Tralfamadorians, who see all of time simultaneously and know that to exist once is to exist forever. The irony of the situation, however, is that Vonnegut has chosen to write a novel in response to the events that he witnessed. And though he may say "so it goes," the novel shows that the deaths have deeply affected Vonnegut, as they have deeply affected Billy Pilgrim.