For the OP I have a couple of comments:
Starting a hike in the back country, especially the mountains, at 17:00 sounds like really bad planning and recklessness. Sunset in the mountains here - Alberta Rockies - was within four minutes of then last weekend. And it gets very dark in these mountains after the sun sets. Even if you have some pretty good head lamps, I would think that humping it up a mountain would be pretty dangerous under those circumstances. If you are going to do something like that regularly, I would suggest that you invest in a personal distress beacon before you worry about a folding saw, so that SAR can more readily locate your body at the bottom of the ravine you slid into.
That being said:
For years, I strapped nothing but an Estwing axe to my pack and used that. Until one rather memorable trip with some friends resulted in a need to make and sustain a good fire. Very difficult with just an axe and no dead-fall above the snow. After we survived and made it back
I bought a 26" bow saw from Canadian Tire, I think for $15-$20. That was many years ago. The Estwing pretty much only sees use when I am car-camping now, but the bow saw still gets carried backpacking.
Even though it is a full size, non-folding saw, it has negligible weight. The blade can be removed, and both pieces can be lashed to your pack in various ways. The 26" blade goes through good sized logs or trees very quickly.
A hatchet replaced the axe. I have several, and the one I use currently is a Fiskars. These days though... I am starting to wonder about replacing the hatchet with a smaller pocket axe or mini-hatchet for all that I use it for now.
I would disagree with you, and I would think that the majority of other people would as well. In fact, I would go so far as to suggest that winter "is" the need for fire. Although it is true that one could probably get by by wearing the proper gear and having a properly insulated shelter, the majority of us are more comfortable living in a home, and working in structures that are heated. Usually by fire. Even the Inuit have pretty much abandoned igloos heated by oil lamps these days.
In the back country, there are many reasons for building fires in the winter.
Had a real interesting experience this weekend on an overnight hunt in 5f/-15c. Got in the woods around 5pm and had an incredibly vigorous 5 hour snowshoe up some very steep mountainous terrain...
Starting a hike in the back country, especially the mountains, at 17:00 sounds like really bad planning and recklessness. Sunset in the mountains here - Alberta Rockies - was within four minutes of then last weekend. And it gets very dark in these mountains after the sun sets. Even if you have some pretty good head lamps, I would think that humping it up a mountain would be pretty dangerous under those circumstances. If you are going to do something like that regularly, I would suggest that you invest in a personal distress beacon before you worry about a folding saw, so that SAR can more readily locate your body at the bottom of the ravine you slid into.

What do you folks find works as a BACKPACKABLE winter wood-processing solution?
For years, I strapped nothing but an Estwing axe to my pack and used that. Until one rather memorable trip with some friends resulted in a need to make and sustain a good fire. Very difficult with just an axe and no dead-fall above the snow. After we survived and made it back

Even though it is a full size, non-folding saw, it has negligible weight. The blade can be removed, and both pieces can be lashed to your pack in various ways. The 26" blade goes through good sized logs or trees very quickly.
A hatchet replaced the axe. I have several, and the one I use currently is a Fiskars. These days though... I am starting to wonder about replacing the hatchet with a smaller pocket axe or mini-hatchet for all that I use it for now.
There's no need for fires in the winter.
I would disagree with you, and I would think that the majority of other people would as well. In fact, I would go so far as to suggest that winter "is" the need for fire. Although it is true that one could probably get by by wearing the proper gear and having a properly insulated shelter, the majority of us are more comfortable living in a home, and working in structures that are heated. Usually by fire. Even the Inuit have pretty much abandoned igloos heated by oil lamps these days.
In the back country, there are many reasons for building fires in the winter.