What does the destruction of the second creature in Frankenstein say about the role of women?
The role of women in Frankenstein is quite delineated: Women are nurturing, loving, supporting, and this is the reason why the creature went straight to Victor's bride to kill her: It knew that Victor regarded her in such high esteem and loved her so much that it would devastate him. And it did.
When Victor destroyed the second creature, he did it under the assumption that the first creature would procreate with the second one. Victor shrieked at the idea that a new race of monsters would come out of such morbid union, and decided not build her. Similarly, the monster wanted the 2nd creature to be created using as his argument that he needed company, and he wanted to have the same chance as Victor to make a life with someone.
However, destroying that second female creature means that the "monster" kind has come to an end, therefore, women have the unique role of bringing life into the world, to permeate the world with life, and to keep the human race going. Not having a female in the story means that the end is near.