First make a firm little scratch on the trunk and if you see green under the bark, it's alive. Second, get a wide tray of some kind with sides of at least 1" high and fill it with stones or anything that won't rust and will support the pot on top. Then fill the tray with water, but not enough to ever touch the pot (or roots could rot). That's for humidity and is much more effective than spraying. Don't water the tree til 1" of the soil on top is dry and only water from above, slowly, til it sinks in and all (lower) roots have had some (not just the top!). Put it either very high right under the skylight, or wherever you have that has the most, brightest sun all day long (a couple of inches below a strong fluorescent light 15 hours a day isn't too much and maybe not always enough). Spray the foliage hard with water (kitchen sprayer or shower) even if more leaves fall off. And then except for watering, leave it alone til spring and see if you get new growth. Let it recover (can take weeks).