While I couldn't see carrying a complete winter bivvy/bedding setup while snowboarding. I would at least be carrying a Heatsheets Emergency Bivvy.

I mean, the clothing snowboarders typically wear provides a lot of insulation and protection versus, say, a pair of jeans. This is already a huge advantage in making a night outdoors survivable vs someone wearing lighter and less weather resistant clothing.

Between the clothing, the bivvy helping to provide some additional insulation and wetness protection, and some pine boughs below and above providing additional insulation I wouldn't doubt it could keep a person alive down to some surprising temperatures. Comfortable, no, but still alive.

With that said, finding/building a proper shelter and building a fire is always going to be your best bet. Even with a good winter bivvy setup, you are still relying on your core heat to keep you warm and alive. This is kind of a loosing battle, as you aren't adding any additional heat beyond what your body can make. Since you probably aren't eating much, if anything, your body is going to have a tough time keeping your core temperature up. Therefore, you are going to have a tough time staying warm.

What makes a fire so important is that it adds heat beyond what your body can provide. Even if you don't have windbreaks/reflectors (which aren't really that hard to make, I mean your snowboard could work as a reflector) a fire can still provide some additional warmth. It also has a secondary psychological benefit, as it gives you something to focus your attention too. Otherwise, you pretty much just dwelling on how cold and probably hungry you are, and if you're out at night...how dark and spooky it is.

Besides that, fire has the potential added benefits of being a signal and a helpful deterrent if any animals come around thinking you might make a good meal.