What do you believe is the authors purpose for adding in Micheal Holtzapfel at the end of the book?

One of Frau Holtzapfel's sons, Michael served in the German Army in the Battle of Stalingrad, where his hand was severely wounded. At a makeshift hospital, he sees his brother Robert die. He returns home and later commits suicide, unable to live with the guilt of having lived while his brother died. I think this is one of the reasons Frau Holtzapfel takes a liking to Liesel. Liesel reminded her of him.