The roots look okay to me. It's hard to give specific advice without knowing which Den it is. Hopefully, it's a deciduous 'chid and losing it's leaves is normal. Keep an eye on it for signs of new growths at the bottom of that cane. Most Dens like high light and keep it a little dryer than it looked in the first pics. Even if it's not a 'chid that should get a winter rest, most chids should have some sort of reduction in water during the winter months.
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