What you have there is Datura metel, a native of India. They'll produce a bunch of bumpy seedpods until late fall (all other species of Datura produce spiny seedpods, except for Datura ceratocaula), and the seeds will either disperse themselves, or you can snip off a ripe pod and dry the seeds for next season. I don't know how it works with Datura metel, but they should self-seed just fine. In fact, many Daturas use the winter to activate their seeds. My Datura inoxia and my wrightii do just fine without intervention, and the area which I live in will frequently drop to the low thirties during the winter. Datura stramonium is a common weed throughout the eastern United States, so the seeds from your plant will do just fine. The plant itself will look pretty miserable during the winter, but it might come back.

Just to be on the safe side, collect the seeds and replant them around the end of winter. The plants love the heat, and will generally die after three or four years, perhaps fewer in colder climates. The good thing is that they produce so many little seeds, you can replant as many as you like year after year.