Usually we are lucky to have more than one or two thaws in a winter. Maybe global warming is cause for hope..
Rabies is a poor comparison, especially when you consider that a human would have to cut the trail of an infected animal and the odds of that are pretty slim, and even more so when you consider the odds of that particular patch of snow being contaminated.
My curiosity with Ebola, though, lies in the concept that humans congregate unlike the more territorial rabies carriers, and share space. Those shared spaces would have a significantly higher possibility of fomite contact, frozen or otherwise, and cold has been shown to preserve the virus. I even cited ER entrances as an area of possible concentration, due to the nature of the traffic there.
While winter is ertainly not at -70C ambient, but I have been in -40 (same temp either scale) and colder weather numerous times, and yes, life goes on despite the cold. I have seen a month here where the high temperature for the month was zero Fahrenheit (on one day, for about an hour), so this isn't the more temperate winter of much of the lower 48 I am talking about. Our snow sublimates during the winter, but seldom melts until spring.
Maybe where you live, the human population density is so low that humans and rabid animals never cross paths.
Here, the rabid animals are right in cities and towns.
The possibility is extremely remote, but *if* an Ebola patient were to show up at a hospital in ND in the dead of winter, and they were vomiting, the hospital would (I hope) be sanitizing the area—regardless of whether Ebola is suspected. There are plenty of nasty viruses that can be present in vomit.
The cold conditions that were shown to preserve the virus were in the controlled conditions of a laboratory. Laboratory freezers and fridges are made so as not to have temperature fluctuations, because those fluctations are very destructive to biological molecules. Winter in ND might be unrelentingly cold, but it does not remain at a stable temperature. Besides that, even in extremely cold temperatures, many enzymes are active, including the RNA destroying enzymes that are ubiquitous in the environment. For storage, viruses are suspended in special pH buffered solutions.
I have attempted to store proteins in a -20C freezer. I had boiled the proteins and added chemicals meant to stop any enzymatic reaction. Yet my proteins became degraded within a month. I can go on and on about the difficulty of preserving biological substances in a lab—the bottom line is that there is little reason to think an inherently unstable virus can somehow be durable in an uncontrolled environment. The temperature changes, the pH changes, variations in humidity, fragility of RNA, and so on, make it very unlikely that it will survive.