During the winter I travel long distances over 25 miles into forest, lakes, rivers and mountains. I always worry that when it's time to leave I'll find myself trapped by tree laying over the road. Temperatures can be 25°F to 45°F (around -5°C to +5°C), and the chances of seeing anyone there could be slim during the winter. Should I activate my beacon?
My first response is "No, you should not set off your beacon, it would interfere with Natural Selection."
Seriously though, if you are not equipped to spend a single night out, you should not be there. Your beacon should be used only in a life threatening emergency, a tree across the road should not be enough on its own to generate the level of peril that your life is in danger. If there is a risk of trees blocking the road, you should carry the tools to clear it, or arrange for someone to come and look for you if you do not return.
It's different if the tree fell on you, or the tree blocked your exit and an unexpected, unseasonable storm came in and you have been trapped for a week, or the tree is blocking your exit and you are being stalked by a pack of wolves. In these cases, it's not unreasonable to call for rescue.
If you aren't equipped to handle a situation where you can't drive out as expected, then you don't belong there. Conversely, if you go to such places and situations, you should take enough stuff with you to be able to survive and possibly get out on your own.
A tree falling across the road is only one of several things that aren't too ridiculously improbable that prevent you from driving out as expected. Something could go wrong with the car. If in winter, a large enough snow storm would prevent driving out. A tree falling across the road isn't even the most likely of these.
If you're going into the forest on backcountry roads 25 miles from the nearest pavement, cell phone reception, etc, then you need to be prepared. The level of preparedness depends on what dangers you will face, how much time you have to deal with them, and what level of hassle and uncomfort you are willing to put up with.
In summer, it might be as simple as bringing a wind breaker or rain coat, and water. You can walk the 25 miles, even if it takes most of the night. For a bit more comfort, bring a small tent. Stay in place until the next morning, then you've got all day to hike out. If further away, bring a backpack with a tent. Now you can take multiple days to hike out.
In winter, warm clothes and a sleeping bag are pretty much essential. Even a "3 season" tent, snow shoes, and backpacking stove are a really good idea. Personally, I wouldn't drive 25 miles into a forest in winter without them. From there, add more to increase comfort. In summer, not eating for a day or two is no big deal. In winter, that's not such a good idea because your body needs more calories just to keep warm. You really should have a few days of food with you.
What you describe actually happened to my, although it was in summer. I drove about 20 miles into the National Forest southwest of Flagstaff Arizona. I did a day hike down into Sycamore Canyon and back. During the last hour on the way back, a strong thunderstorm rolled in. It came with some serious wind, lightning, and rain. I got back to the car about 15 minutes after it was over. At that point it was about 17:00, which meant about 2½ hours of daylight left.
Shortly after leaving the parking area, I encountered a large tree across the road. There is a whole network of "roads" in that area, so I looked at the map and planned to take a longer way around on somewhat less desirable roads. I had a rental car with only typical ground clearance for a passenger car.
As I was turning around on the narrow dirt road, apparently the oil pan hit a rock in the road I didn't see. I smelled the oil, then noticed the oil light coming on a few seconds later. I shut off the engine immediately, and coasted down a small hill to "park" the car on the side of the dirt road.
I set up the tent in a nearby spot, had dinner, and spent the night there. It was really no different than what I was planning on doing anyway, just not in that spot. The next morning at dawn, I mixed up a gallon of diluted Gatorade, threw it into a day pack and started hiking out. After about 10 miles, I ran into someone that gave me a lift to the nearest paved road. From there I walked to the police station and told them about the down tree. Then I had to find someone to tow the car, and a place to tow it to where it could get fixed. That took a lot more walking around, but by the time I got back to the car in a tow truck, the tree had been cleared. The car got towed out of there to a garage in Flagstaff, all before it got dark.
Having the equipment and food to stay out in the forest for several days and to hike out if needed, made this just a adventure instead of a serious problem. I never felt like I was in danger or in any real trouble. In this case, the most important item was probably the water and Gatorade powder. The rest made things more comfortable, but without enough water I would have been in at least some trouble.
Different conditions require different items. Think about what you would need and/or want to stay out a extra few days, and to hike out on your own.
I assume here that you are traveling by car.
Make sure you carry a survival package so you can survive for at least a night.
As for the tree situation, carry a large towing strap and invest in a (chain) saw appropriate for the size of trees in the area. This way you should be able to chop the tree in a few pieces and pull them to the side of the road using either your car with the towing strap or by hand.
Do not activate your beacon until you are in actual danger.