I would argue that the ending of Herland tells us that while not all men are capable of change, some are. At the beginning of our story, Terry Nicholson is best described as a misogynist, while Jeff Margrave idolizes women. Vandyck Jennings wishes to study women from a sociological perspective while having no real understanding of them.
A foreshadow of the novel's end can be seen in the men's attitudes when they are imprisoned and given lessons by the women of Herland. While Jeff and Vandyck try to learn, absorb, and adapt to their new surroundings, Terry reacts like a control freak and becomes angrier and more anxious by the day. He is rude to his captors and continues to be condescending towards women in general.
Ultimately, all three of the foreign men fall in love with Herland woman and marry, not realizing that the Herland women's definition of marriage is drastically different to their own. According to their new wives, there will be no sex, no changing of surnames, and no cohabitation.
As transformed, enlightened men, Vandyck and Jeff settle into their new marriages with varying levels of emotion and contentment. Our misogynist, Terry, cannot accept the nature of his marriage. He attempts to rape his wife, which, of course, the woman of Herland do not take kindly to. Terry ends up being banished from the country.
In a nutshell, much changes in this novel in terms of Vandyck and Jeff's lives and their appreciation of women. Life changes, too, for the women of Herland, as they will now witness the first pregnancy in two thousand years to have been the product of a man and a woman. Since Jeff decides to remain in Herland, there will now be a man living here for the first time.