grumpy-- I am a Wildlife Rehabber--I know the difference between torpor and hibernation, and I saw the research on tagged possums-- they actually migrated from equatorial regions ( more likely were carried accidently same as the armadillo). Anyway-- yes, they torpor, as do bears. The winters this far north are VERY difficult for them to get through- it is rather hard for them to wade through snow that is deeper than they are tall, and unless they find a nice warm building with a free flowing food supply nearby, the warmer spells do not last long enough for them to replenish used calories. Our resident possum at the rehab center lived 15 years- and getting her through winter was an interesting balancing act- do we put food out today, or not? She was normally too grouchy for us to disturb if we saw signs of overnight activity- but we did not want to put out food and have her leave it- thereby attracting the 'wild' possums and winding up with 'patients' because they found the food, and could not get to it, exposing themselves to the hypothermia potential.
The powers that be- found out the HARD WAY- NEVER wake up a groundhog for Groundhog Day activities-(a true hibernator) it WILL kill them. (Punxatawny Phil has a light and heat regulated burrow, most don't)
Anyway, Virginia was succeeded by Marcy- and it was a planned succession, as Virginia died of Aspergillosis before Marcy's first winter- Poor Virginia had been under the weather all summer- Marcy was chosen from one of the first possum litters from a 'hit by car' possum mom, and was tubed until her mouth formed and she would have crept from the pouch.