That’s what happened when a previous cat of mine, who I let outside, was treed by a neighbor’s dog. When the neighbor kids told me that I needed to call the fire department because she was stuck in that tree, I replied, “She got herself up there, and she can get herself down.” I did see her slide headfirst down that tree trunk, and then she patted on the door and I let her in.
Quite a lot of the cats would die too. The life expectancy of an entirely feral cat with no human support is a lot less than that of a cared-for cat; plus which, most current domesticated cats have no experience taking care of themselves, and many of them wouldn’t survive the learning curve.
– I’ve seen an inexperienced cat fall out of a tree – she’d put her weight on a dead branch, and it broke under her. She wasn’t significantly injured, having not fallen very far; but they certainly can fall, and there’s no guarantee they won’t be hurt.
My dog treed a cat a few years ago; the cat then either fell or jumped out of the tree and was at least stunned on landing. Dog dispatched the injured cat before I could intervene. 
Anecdotal data point. In the Mara Triangle in Kenya last summer, I watched two lions (young males) climb a tree to presumably get away from the flies (the guides said that this was unusual behavior and more common to some Tanzanian and further south lion populations, but they had been seeing it more and more over the years.) It was also a good vantage point over the wildebeest herd which was just arriving. Both got comfortable on various branches, and then after 5 minutes one of the two saw something and jumped down. And as I was standing in an open roofed vehicle (10’?) and was looking up to see the lion, he was at an absolute minimum of 15’ but I would have said 25’ confidently. And he hit the ground running!
Wild cats are powerful! Those legs and claws hold onto buffalo, etc. for hours holding up the cat’s weight. The lion (not known to be a tree climber or as sleek as other cats) just absorbed the fall without any recovery. There wasn’t even a “WHUMP!” from the impact.
So I can anecdotally state with authority, wild cats are not going to get stuck in a tree!
When we were looking at a tiger climbing a tree, and the interlocutor was explaining that they didn’t have a taller climbing tree because a tiger could get hurt jumping down if it climbed too high – that tiger was already at something over 15’ off the ground, and not yet at the top.
Answered in one (at least, my old man was fond of tossing out that fact when I was a wee sprog).
Fast forward 40 years. The Missus: “Looks like Max is stuck in the tree. Someone should probably get him down.” The one true rebuttal to that call for aid falls on deaf ears. So I gets the ladder. Now this is a big ash tree that grows through the middle of our back deck. So the ladder sits on a nice flat surface and the top is resting at the first major fork about 20 feet up. Very sturdy. Up I scrambles. Max trots down the limb, happy to see his favorite monkey has come to join him in this arboreal refuge. We talk a bit, do some head boops and a nose rub. I offer to scruff him down but he politely declines and shows me this cool trick he learned where he buries his claws into the tree bark and is essentially part of the tree. Maybe he was afraid, or maybe he was psychic and afraid, because just as I let go of his neck and we were agreeing he would come down by nightfall because Mama is worried (we both roll our eyes), the 20+ year old prefab deck board failed, the ladder pitched sharply and down I went. At the ER, after he’d given up trying to set my elbow, the otherwise knowledgeable physician told me of a trick he knew about using a ladder to get a cat out of a tree. “Bring the ladder over to the tree, and just throw it hard to the ground. The noise will convince the cat there is a quieter place inside the house and will end up there in just under 5 seconds.” I believe this is what actually happened. For nobody else ventured up to get Max, but he was waiting for me on the couch when I got home.
If you have a ladder, and can raise it against the tree, why not just leave it there and let the cat figure out the rest? Most cats are perfectly fine with using aluminum ladders to climb up or down (and wooden ladders might suit them even better)!
But what if the cat is in a box?
Well, Stephen Maturin in Patrick O’Brians The Nutmeg of Consolation has this to say on the subject (when two small girls are “stuck” high up in the rigging)
My cat has a remarkable propensity for uttering heart-rending complaints because he is “stuck” and can’t come in from outside, even when the door is standing wide open. He also likes to be fed, even if there is a full bowl of food in front of him. He doesn’t want food. He wants to be fed!
Is there such a thing as a cat that does exactly what you want, when you want it to? 
When have I ever held myself out as someone who thinks things through?
I’ve only known one cat who would climb ladders; though that one cat seems entirely comfortable on them, whichever direction he’s headed in.
The human who’s trying to come down the ladder and finds a cat taking up all the space on the next rung down may be less comfortable about it, however.
[ETA: That particular cat doesn’t get stuck in trees, either. I doubt that a cat who’s comfortable coming down a ladder is going to be uncomfortable coming down from a tree. Ladder rung spacing is designed for humans, not cats.]
Eh, I have seen cats climb up and down ladders like it was the most natural thing in the world, as well as sit on the rungs. You may be onto something that obviously those cats know how to climb trees quite well, but an inexperienced or frightened cat might well be quicker to climb down a ladder, or piece of lumber acting as a ramp, than leap a great distance to the ground.
Cats do not just get stuck up trees, though. There are also balconies, rooftops, scaffolding, silos, construction sites, etc., (curiosity killed the cat, after all), and sometimes they absolutely need to be rescued. There is an entire Youtube channel about it, though they are mostly about trees and pets, and sometimes the cats do successfully climb down.
How about adog that got stuck chasing a cat up a tree? (Dog required rescue, cat came down on its own.)
Let’s bear in mind that cats have nine lives. (I assume that’s just a statistical average.) So if, say, a cat starves while stuck up a tree, or falls and gets eaten by Fido, that’s just one life down. A cat may expend multiple lives by the time it figures out how to get down on its own. So as long as a cat has a few lives left to go, it has a good chance of finding its own way down within its remaining life-count.
It must take quite a lot of curiosity to kill a cat.
What about bears? They climb trees too. Does anyone know how bears get down from trees? Do pampered pet bears get stuck in trees more than wild bears?
Definitely true.
I had a cat get stuck on a neighbor’s roof, years ago. The cat had probably gotten up there by way of an overhanging tree, and had very likely climbed out on a branch which bent under her weight to near the roof, jumped off onto the roof, and then found that the branch had sprung back up to a position out of her reach.
The neighbor managed to get her in through an attic window, and then put her out of their house via the stairs and a door. But if they hadn’t been willing to open the window for her (or at least allow a ladder), she’d have had to jump down two stories onto hard ground, and might well have been injured.
Basically the same way they got up, just by backing down.
My understanding is they get killed by Davy Crockett.
Those would be bars, not bears.
When I was a very young child, I always got a very strange visual image in my mind of what was going on when I heard that.
Maybe I’ve only been possessed by supercats. None has been stuck on a roof or tree. Kittens swarmed the oaks. Adults climbed up and down roof ladders. Some didn’t bother with any of that, but stayed grounded. They must be the smart ones.