When an idea is not flowing naturally, the best thing to do is to completely change gears and let it go for a while. It is hard to find a cliche or common expression that would summarize such a shocking disappointment in Biff Loman's life. After all, he has just witnessed, according to the entry, his much-idolized father falling from the height of Biff's supreme admiration.
An idea that you could consider is to focus on Willy as the antihero in Death of a Salesman that fought his entire life to create the image of a hero. Not only did he want to make himself believe that he was a successful man, but he instilled the same delusional idea into the overall psyche of his family. As a result, Willy is respected and almost feared within his household, precisely because he continues to put this heroic front of someone that he has never truly become.
Someone who claims a trait of superiority, and then proves to be anything but superior, is often referred to as a "king of clay", or as a "saint of clay". Basically, this metaphor alludes to the fact that these types of people are as weak, feeble, and "breakable", as anybody else. Moreover, it also implies that they can be easily pushed out of the pedestal that society, or themselves, have created because they are hollow and quite useless inside. This being said, an idea for a title would be "The Fall of the King of Clay" or "Even Kings are Made of Clay". You could also refer to the fall itself as "The Deepest Fall of All". Also, could focus on Willy as a king that has fallen from grace and title the entry "The Disgraced King", or merely use suspense by adding three periods and title the entry "...Disgraceful" and leave it at that.
You have a lot of material to gather ideas from, so do not focus your attention on form, but on the content of the title and that should make it easier for you.