The Kia/Hyundai batteries tend to do very little in the way of degradation. So you should be fine in that sense, even in 6 years time. As for the use of heating or cooling, as long as you do the usual things like preheating your car before departure, and are willing to set the climate to a comfortable temperature, and not hot - This again should be fine too.
You're looking at a touch over 3 Miles per kWh needed to achieve 200 miles. In a car like the Niro that shouldn't be too hard to do at all, but in the very worst weather (sub-zero temperatures, strong winds, snow and ice etc.) then you may need to accept that dropping your speed or stopping for a brief rapid charge could be necessary.
I Don't own one of these cars myself, but based on my knowledge of it's sibling the Kona, and a few chances I had to play with the Niro that would be my guess. Hopefully someone will be along soon who has had the chance to put this to the test in bad winter conditions and can speak with their personal experience of this to either confirm or deny my suggestions for you for sure.