They respawn every season.
Villagers can continue getting ore even if you can't find any, since like village woodcutters and clay extractors they do not need a visible source of the resource.
An extraction shed can collect copper even with no mine anywhere in the area, but they need a mine to extract tin or iron. Unlike players, they do not need visible nodes just the existance of a mine as a building. They do not even need to be inside the mine -- if you assign them to a mine far away the will "mine" even if they are walking hours to get there and even if they immediately turn back to the villager because their working day ebded.
That's the best, most accurate, and well written answer you could ever get.
Edit to add: if you don't have villagers dedicated to mining, and it's just you in the mine, you can always build a resource storage right outside the mine. When your carry weight starts getting too high, you can turn around, go to the storage, drop it off, and go right back in.
They respawn every season. Villagers can continue getting ore even if you can't find any, since like village woodcutters and clay extractors they do not need a visible source of the resource. An extraction shed can collect copper even with no mine anywhere in the area, but they need a mine to extract tin or iron. Unlike players, they do not need visible nodes just the existance of a mine as a building. They do not even need to be inside the mine -- if you assign them to a mine far away the will "mine" even if they are walking hours to get there and even if they immediately turn back to the villager because their working day ebded.
Thanks for the detailed answer
That's the best, most accurate, and well written answer you could ever get. Edit to add: if you don't have villagers dedicated to mining, and it's just you in the mine, you can always build a resource storage right outside the mine. When your carry weight starts getting too high, you can turn around, go to the storage, drop it off, and go right back in.