The cake is symbolic of Miss Havisham's wasted life. It could also be symbolic of death and devastation.
Explanation:
It depicts the numbers of isolation and administration is Miss Havisham. For most of her life, she has denied to let go of her past as she advances to wear her wedding clothes and keep her marriage cake. Her falling dress and cake are representations of how her life disintegrated away. It also represented the state of the Satis House, where she remained hidden from the remainder of society. The house is used as a comparison to show how they died and broke as time passed on
