So I come home from grocery shopping Friday evening while it is still somewhat light out. I leave the passenger door ajar to remind me to move my snowbrush to the trunk, but as I unload it drifts shut. I park and go inside for the evening. I fall asleep on the couch and at about 4 AM I hear the sound of slabs of snow falling off the roof. At least, I’m relatively sure that’s what it is, but I get up to investigate. Lo and behold, my interior light is on. I slog out and shut the passenger door, and verify that my car still starts.
Later I realized how lucky I was. I was hunkered down with fresh food and DVDs and didn’t leave the house again until 11:00 AM on Sunday. I also didn’t get up until 12:30 PM Saturday so in the daylight I never would have noticed the light was on. My car complained a little but started up on Sunday.
I’m really lucky that snow decided to give way.
I also bought a new battery for the car, just in case. (The old one is pretty old; I do realize I don’t need to change a drained battery. 
)