The earth regenerates metal in a lot of these types of settings. Otherwise, how would the Norse still be using bog iron? That stuff is characterized by being easily exploitable but limited in amount. Unless the bogs were ten times the size, they'd be tapped in a tenth of the time, and this world isn't the size of Jupiter like they are in some Xianxia.3RFS is much more convenient and provides better goods, right up until 3RFS dies in a fight, and then 3RFS is much less convenient to replace. Also 3RFS sucked up all the near-surface metal and didn't leave a tunnel to getting the metal further in, like a mine would.
So mines might actually just last indefinitely and a miner could just be a different sort of farmer from an economics perspective for all we know.