Now we're drifting from "the problem with Ravenloft is you can't win" to "the problem with Ravenloft is it's an artificial world." Different argument, but I'll still take it on.
IMHO, Ravenloft's artificiality is one of its strengths and adds to its uniqueness as a game world, and it's usuability by DMs.
Just because there's a new darklord in the domain doens't mean they are instantly in charge. Mordent, Lamordia, and Nova Vaasa, for example, all have political leaders that are not the darklord. In all three cases, the darklord lurks at the fringes of power, and in the case of the first two, the political leaders are even relatively benevolent. There's nothing stopping the PCs from crafting such a society in Strahd-less Barovia. Heck, if they can defeat Strahd, they can probably do so even without killing him, just deposing him. There ARE (relatively) safe havens in Ravenloft, Mordentshire being the foremost.
In any case, unless the DM goes with the "Barovia and everything in it dissolves" possibility, killing Strahd is always a change for the better. No matter how many darklords may take his place, no matter if Strahd Rises from the Grave, there's one less bloodsucker for a while, and THAT'S A VICTORY.
A concrete, canon example: The people of Gundarak may not appreciate being second-class citizens in Barovia, but they are far better off than when Duke Gundar was alive. (er... undead... er... the first time around... let's just say "when Duke Gundar was darklord of Gundarak".) At least they don't have to worry about their daughters being seized by their ruler. (Unless she's the latest Tatyana reincarnation, I guess, but for the most part, no.). They are utterly unaware of the metaphysical underpinings that changed in their land. Just that one tyrant was slain, and a neighboring, less brutal one took his land. The ones on the Invidia side of the border were even better off, at least until Malocchio took over. But that's situational. If someone killed Von Kharkov, for example, and his domain was absorbed by Mordent, the Valachani would be way better off. And it can happen. Gundarak is the proof.
1) The realms don't shift on a daily basis. There was one major reshuffling during the Grand Conjunction, a single catclysmic event that hasn't been repeated. Cataclysms are supposed to change the world in fantasy settings. Just ask the people of Krynn, or Atlantis, or Dominaria, or Alderaan. Other than that one time, there have been the addition of new lands, including new seas, but except in the infancy of the demiplane, these have occurred simply by the Mists rolling back and revealing new land, whose inhabitants claim it was "always there."
2) Nitpick: Drakov can't close his borders. But if another DL were to do so, disrupting trade, how is that different than a dragon preying on trade routes or magic ritual gone awry making a road impassible? These things happen rarely, but this is a fantasy world.
3) The really weird stuff like the moons has been smoothed over in recent editions of the setting. Nova Vaasa's five moons were debunked in Gazetteer V, and Sithicus, which used to have only Nuitari, the black moon only evil people can see, gained a normal moon as well as of Spectre of the Black Rose.
4) Cultural advancements take time to spread, and the Core simply hasn't existed together for very long. Add to that the natural resistance to long distance travel of the average peasant and the added danger of such travel in a horror-fantasy world, and you can easily have different cultures side-by-side.
5) Much work has been done in the 3e line to bind the world together as a cohesive whole. Just because the domains started separately doesn't mean they have to remain that way. The Ezran religion has spread across the Core, diplomacy between the domians has become important.
The climate issue is, admittedly, a little weird, but much like the Misty Borders themselves, and the "new lands" being revealed, the people of Ravenloft have no reason to think this is unusual. This is the only world they know; the science of even the most advanced domains doesn't go much further than Earth's 1800's. If it's the way it's always been, it would seem perfectly normal. The "ends of the earth" is a real tangible place in Ravenloft and the demiplane is a world that's just a little closer in time to its creation "myth" than most. And if you're a Barovian farmer for whom a long trip is to the marketplace in town, who cares? PCs are a different breed, of course, and in the course of their adventures may naturally start to figure out something weird is going on. But does that make it less worthwhile to save the day?

Depends, one of 3 things. From the FraternityofShadows.com FAQ:In Ravenloft proper, What becomes of a domain once its darklord is destroyed?
I would add "the domain disppears" doesn't necessarily mean everyone in it disappears. For domains that were pulled from Prime Material worlds, it could mean the whole land returns to the world it came from.
- The domain disappears (most likely with smaller Island-type domains).
- A nearby domain absorbs the land (as occurred with Gundarak during the Grand Conjunction).
- Some other evil being in the domain takes over the Lordship. (as occurred in Richemulot and Invidia).
Depends, could be any one of the above. And it's up the DM to decide. Since we know from the Roots of Evil module that the original Barovia still exists in the Prime Material plane, it probably wouldn't go back there. But I doubt it would dissolve, being part of the Core. Most likely I'd say absorbed by its neighbors as Gundarak was. Or perhaps falling to another darklord, likely Lyssa von Zarovich. But either of those situations is likely a change for the better.If the PCs manage to kill Strahd, what happens to Barovia? Could the PCs try to hold Barovia and make it a better place? If not the domain, how about establishing a safe-haven in the domain? In ANY domain?
Just because there's a new darklord in the domain doens't mean they are instantly in charge. Mordent, Lamordia, and Nova Vaasa, for example, all have political leaders that are not the darklord. In all three cases, the darklord lurks at the fringes of power, and in the case of the first two, the political leaders are even relatively benevolent. There's nothing stopping the PCs from crafting such a society in Strahd-less Barovia. Heck, if they can defeat Strahd, they can probably do so even without killing him, just deposing him. There ARE (relatively) safe havens in Ravenloft, Mordentshire being the foremost.
In any case, unless the DM goes with the "Barovia and everything in it dissolves" possibility, killing Strahd is always a change for the better. No matter how many darklords may take his place, no matter if Strahd Rises from the Grave, there's one less bloodsucker for a while, and THAT'S A VICTORY.
A concrete, canon example: The people of Gundarak may not appreciate being second-class citizens in Barovia, but they are far better off than when Duke Gundar was alive. (er... undead... er... the first time around... let's just say "when Duke Gundar was darklord of Gundarak".) At least they don't have to worry about their daughters being seized by their ruler. (Unless she's the latest Tatyana reincarnation, I guess, but for the most part, no.). They are utterly unaware of the metaphysical underpinings that changed in their land. Just that one tyrant was slain, and a neighboring, less brutal one took his land. The ones on the Invidia side of the border were even better off, at least until Malocchio took over. But that's situational. If someone killed Von Kharkov, for example, and his domain was absorbed by Mordent, the Valachani would be way better off. And it can happen. Gundarak is the proof.
The "patchwork vs. real world" argument is one that has raged among Ravenloft fans for years, and if an artificial world isn't your cup of tea, I'm not likely to convince you otherwise, but there a few misconceptions here.The point in subtle, but its there. Gothic Earth still conforms to Earth standards; there are no magically appearing seas every just accepts, portions of Africa don't go missing one day, trade isn't interrupted because Lord Drakov is having a hissy-fit and closing his borders, and the racial, cultural, and technological advancements (let alone weirdness like moon changing from domain to domain) of the world don't radically shift by walking from Spain to Turkey. Too much of Ravenloft is cliche stitched together without rhyme or reason creating a world that doesn't FEEL natural, even to a native. Its a collection of pieces, not a harmonious whole.
1) The realms don't shift on a daily basis. There was one major reshuffling during the Grand Conjunction, a single catclysmic event that hasn't been repeated. Cataclysms are supposed to change the world in fantasy settings. Just ask the people of Krynn, or Atlantis, or Dominaria, or Alderaan. Other than that one time, there have been the addition of new lands, including new seas, but except in the infancy of the demiplane, these have occurred simply by the Mists rolling back and revealing new land, whose inhabitants claim it was "always there."
2) Nitpick: Drakov can't close his borders. But if another DL were to do so, disrupting trade, how is that different than a dragon preying on trade routes or magic ritual gone awry making a road impassible? These things happen rarely, but this is a fantasy world.
3) The really weird stuff like the moons has been smoothed over in recent editions of the setting. Nova Vaasa's five moons were debunked in Gazetteer V, and Sithicus, which used to have only Nuitari, the black moon only evil people can see, gained a normal moon as well as of Spectre of the Black Rose.
4) Cultural advancements take time to spread, and the Core simply hasn't existed together for very long. Add to that the natural resistance to long distance travel of the average peasant and the added danger of such travel in a horror-fantasy world, and you can easily have different cultures side-by-side.
5) Much work has been done in the 3e line to bind the world together as a cohesive whole. Just because the domains started separately doesn't mean they have to remain that way. The Ezran religion has spread across the Core, diplomacy between the domians has become important.
The climate issue is, admittedly, a little weird, but much like the Misty Borders themselves, and the "new lands" being revealed, the people of Ravenloft have no reason to think this is unusual. This is the only world they know; the science of even the most advanced domains doesn't go much further than Earth's 1800's. If it's the way it's always been, it would seem perfectly normal. The "ends of the earth" is a real tangible place in Ravenloft and the demiplane is a world that's just a little closer in time to its creation "myth" than most. And if you're a Barovian farmer for whom a long trip is to the marketplace in town, who cares? PCs are a different breed, of course, and in the course of their adventures may naturally start to figure out something weird is going on. But does that make it less worthwhile to save the day?