Cabanes are (small) buildings without fancy facilities. They are meant to keep you dry, that is all. And that is precisely what we are looking for since we did not bring a tent along. And even if you did, you might prefer a cabane to your tent when the going gets tough.
No fancy furniture, no cosy beds, no electricity, no TV, no radio, no fridge, and nothing else as well. If you are lucky, you might find some sort of table, something to sit on, a few kitchen tools, as well as memories and other things left behind by previous visitors. If there is more than this, you are either very lucky, entered a cabane used by a shepherd during the season, or found an unguarded refuge rather than a cabane. Click on the image if you want a visual impression of a typical cabane interior. Did you notice the candles and the broom? Well, do not be afraid to use the latter for leaving the cabane in a (more) proper state for the next visitors. And you could also take along a candle to replace the one you used last night. The next visitors will certainly appreciate these kind of gestures. Whatever place you visit, remember that you will be the next visitor somewhere else later on and appreciate these kind of gestures too.
If there is a stove (the luxury!) or fireplace, you could cook a simple meal. Or warm up that awful instant food you brought along, so that it tastes less awful. You could also use it to warm the cabane itself, so you won't have to unpack your paraglider to keep you warm at night. Just be aware that you will need to get the firewood yourself. Even if there is some firewood, leave it for an emergency and collect your own. This means you will have some work to do, especially if the cabane is above the tree line. But there is usually plenty of time for that.
Before tourism arrived, people actually lived and worked in the mountains. Whole villages existed in complete autonomy, isolated from the rest of the region. People were needed in greater number than today, since there were no or few suitable machines to do the work. Mostly farmers and shepherds, which are still there, but also custom officers, gendarmes, soldiers, transporters, carriers, backers, priests, carpenters, miners, smugglers, and so on. Now we have machines to do the work single handedly, or we simply abandoned the work that had to be done at that time.
The people may have gone, but the remains of that period are still visible. Often as nothing more than a pile of stones or a change in vegetation. Some of those remains can be used as shelter though. A cabane might be (part of an) ancient fort or factory, a ruined farm, a former workers shed, an abandoned building in a small (thus no longer profitable) ski resort that has been closed, et cetera.
A cabane may also have been built for tourism on purpose. Or it may not be there at all, even though it is indicated as such by maps and signs. After a long day of hiking in Les Écrins once, I was looking forward to sleeping in the cabane that was shown on my map and indicated by the signs I was passing along the way. The light was already fading (hence the not so good image quality), when I stumbled upon a ruin. It turned out that the promised cabane was little more than a pile of wood stacked against the only wall still standing. Fortunately, someone had taken the time to put one of the signposts up against this ruin. If it had not been there, maybe I would have continued my hike in order to find the non-existent cabane I was looking for.
In your ordinary life, an event like this could lead to all kinds of unpleasant actions such as suing the map company ("What is the use of using a map if it ain't correct?"), suing the cabane owner and builder ("I could have died from falling shelves that night! This awful cabane is simply too shackle and certainly not ISO blablabla mumblemumble certified."), or complaints to whomever wants to hear them ("I could have died from sneezing that night because that bloody cabane was soooooo drafty."). However, all these kind of actions will not miraculously rebuild the cabane. In order to have a pleasant night, instead of a complaining one, the best thing you can do in real life is to adapt. Adapt and improve! (Motto of The Pilots of the Round Thermal.) In this case, after considering the weather I expected and the risk of wooden shelves burying me, I preferred to spend the night outside. Which was a pleasant affair indeed, having a Lark above me dancing through the sky, singing the last sunbeams away that were setting the snow on Sirac on fire. Rain however, would have given a different scenario. When sleeping outside to admire the stars might not be the best plan that night, then try to (partially) rebuild the cabane or build your own from the debris. Our little ruin for example, has some room for improvement. If you do not have the skills or the energy to (re-)build the cabane, you could use the only wall still standing to keep you out of a cold wind. Be sure to keep enough distance from the wall in order not to get hit by falling debris! From a statistical point of view the chances thereof are small. But a stone that has been in this wall since it construction, might suddenly feel the urge to fall out after 54.783,8 days when it sees you sleeping next to the wall, instead of waiting for its mathematically predicted erosion date of 80.000 days after its construction.
The point I am trying to make is that the forces that shaped those beautiful mountains (i.e. the forces that already transformed zillions of tons of hard, rock solid mountains into smaller units and dumped them in the ocean), have no problem in doing the same to a cabane. Or any other shelter for that matter. A cabane is just one of the many temporary irregularities in the landscape that will be eroded by the elements in a short time if it is not adequately maintained. Do not get caught up in this process.
So, even if it is indicated on the map, I do not count on a cabane to be there. Only if I have been there recently, I will more or less rely on its presence. In this way, I am mentally prepared for a night out in the open. If the cabane is there, it is a pleasant surprise.
A final word of warning: even if the cabane is there, do not count on reaching it that day. I know quite a few cabanes throughout the French Alps, so there should not be any reason to sleep outside other than occasionally. But somehow I often seem to land in the middle of nowhere, or just in between two cabanes that are both too far away to reach that day. It can also happen that, according to your map, you are very close to a cabane but that it is just too far away. For example, the cabane might be one centimetre away on your 1:100.000 scale map. One kilometre only. You start looking forward to a comfortable night and a warm fire, while the (now approaching) rain will gently be drumming on the roof. Unfortunately, that one kilometre could happen to be 1200 m lower or higher than where you currently are. I am not going to descend 1200 m (or even half of that) and walk up again the next morning, only to have a roof over my head. Unless it rains cows and sheep that is.