Your roses might not be dead; there could be live cane below the soil line, or at the soil line. I would prune off the dead wood, and see what happens this spring. I'm not familiar with Don Juan, but it might be prone to dieback in a cold zone.

Many large sorta hardy Japanese maples suffered greatly in zone six st louis. We saw our -10 I believe and were steady cold most of January. Not unheard of but even trees right up next to houses have severe die back. I am trying to notice if I see any wounds or other signs of long term problems on these trees. Something is in my head like "a healthy japanese maple is zone six hardy. Take away some hitpoints with drought or a wound and it is only zone seven hardy." I know my nyssa sylvatica transplants are zone six hardy now but that first winter after transplant everyone has suffered. Salt and de icer are other possible suspects...... Oh, I have a dogwood and three hollies which looked dead three weeks ago. Two are showing a few leaves. Not sure if your tree will do the same. Many of the dead looking Japanese maples around here have SOME new foliage by now.

Paul3: Yes, consistently (little variation) dark (not really extremely dark), cool, dry are very important for dormancy storage of bananas. The interactions of light with non-freezing but low temperature causes chilling injury in most tropical plants which can progress to cell tissue death and subsequent attack by molds and fungi. What happens in this case is that when light strikes the leaves or stems or any photsynthetic tissues, the electrons gets fired up. But the low temperature lowers metabolic activities such that there are no active electron acceptors down the photosynthetic factory. The excited electrons when its energy cannot be diffused would literally damage tissues around it. Damaged tissues are susceptible to attack by fungi or bacteria. Only small wattage light are okay to use, and intermittently only when you need it. The dryness is important to discourage rotting away the corm. The cool is something natural during winter time and induces dormancy of tropical plants as long as it is non-freezing. These three things should be played out in balance. I have kept mine in garage where I have stable temperature that varies only by 10 deg F every day (45 deg F to 55 deg F) during the winter. If your attic temperature varies only by 10 deg F during the entire 24 hours, then that should be okay.

Do you check the humidity? Any chance the humidity is too low in your basement? When I had roses rooting in my basement under lights, I kept them in a larger plastic basket and kept plastic over the top so they stayed pretty humid (in the 80's). Also the basket had an inch of damp pebbles in the bottom. If you don't already have one, Walmart sells a little digital thermometer for less than $10 that gives temp and humidity. It might give you some clues about what is happening. I'm also using plain cheap fluorscent tubes in my sunroom to augment the natural light - but I use the "natural daylight" type. Cheers, Michelle