How does Fitzgerald portray Americans coping with life after the Roaring Twenties?

Fitzgerald's characters in "Babylon Revisited" give the impression of being washed out, exhausted by the past, now trying to deal with an uncertain future. The bubble has burst for Charlie Wales. With his wife dead and his child in the custody of his hostile sister-in-law, Charlie contemplates his high-living past—before the market crashed—when he was flush with money. Paris has become a kind of ghost town to him. His friends have gone or have cracked up. Though he says he's making money "in Prague," his life is one in which the bottom has dropped out, and (as Fitzgerald himself wrote later in "The Crack-up") his is a dark soul in which "it's always three o'clock in the morning."
The one thing keeping Charlie alive is his love for his daughter Honoria. Charlie's sister-in-law is embittered and blames Charlie for her sister's death, but she and her husband have a degree of stability in their lives in raising their own children and Honoria. What enables them to cope with depressing circumstances is familial love; in this sense, they are linked to Charlie, in spite of their never having had the wealth and reckless lifestyle Charlie had in the past.
A chance intrusion by friends from that wild past causes the sister-in-law, Marion, to reverse her decision to give custody of Honoria to Charlie. Those friends, Lorraine and Duncan, are emblems of a superseded life, who drink to anesthetize themselves. This is their coping mechanism, one which Charlie previously used, even in his period before the financial debacle that ended the illusory life he led.
Disillusionment is a frequent theme, of course, in Fitzgerald's work. Even in his earlier writings, while he was flying high in his career and social life, there is a sense of foreboding, a subtext embodying a prophecy of collapse and doom. In "The Diamond as Big as the Ritz," the fortress of wealth and illusion created by the Washington family is blown to smithereens. In The Great Gatsby, the self-made millionaire's life, also largely one of illusion, is destroyed both by Gatsby's weaknesses and, perhaps more significantly, by sheer chance. "Babylon Revisited" is an even more focused vision of the sense of loss experienced by those whose lives of wealth and splendor have been destroyed.