When a religious community no longer has sufficient members to be viable, they usually search for a compatible partner. Thus, a Franciscan community of sisters may merge into a larger Franciscan community, especially one that is "on the same page" in terms of contemporary issues, as well as the Franciscan or whatever charism of origin. Thus, in NY State Franciscan communities in various cities, that were independent orders, formed the Franciscans of the Neuwman communities, which in term absorbed at least one tiny independent Franciscan community, Franciscan Missionaries of the Divine Child, that was dying out. In other areas, you have many now diminished Sisters of Mercy communities, that were independent, merging into a national confederation - in effect, one religious community across the US.
This is what you will find in most cases; the religious order does not go totally extinct, but retains some limited continuing identity in another similar order that goes on. To put it another way, what is happening now is often just a repeal of the splitting process that happened 100 years ago, when communities were bursting with women or men, and formed independent communities for various reasons, often geographic.