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Being that you are in 8a, you could certainly plunk them back into the ground as long as you mulch them really well once it gets colder at night. You could also set them into a pot in the house, tapering off watering over a week or two. The greens will die back and you'll end up with the root system only and then you can plant them in the spring as though you divided them in the late winter. I'd go with the first option, and I'm in 7b, but I suppose it's really just a matter of how much you want to risk.
Oh heavens no not wasting your time .. just put them back in the ground and heavily mulching really isn't necessary .. they look like hedychiums which are tough as nails. I've had them come back after just laying on the surface all winter.
The hedychiums are the first to show up for me .. then the costus and the curcuma is last. Water is the key .. we had a lot of rain this spring and early summer and they grew taller and bloomed earlier than I've ever seen before. As I said, these guys are very, VERY hardy in my zone 8 and they aren't in a protected area either.