I have grown ornamental sweet potatoes this summer and just love the foliage. The ornamental sweet potato is not hardy and will not survive the winter.
Most people just enjoy the plant and let it die come winter.
For those that like a challenge you may be able to start your own next spring. Like all sweet potatoes they produce a tuber in the soil. Dig up the tubers and store over the winter. Keep them cool and dry. Come early spring, force shoots to emerge from the sweet potato.