In Europe, most of towns are historic, they're in good places and can take any place in economic system.
In America, there are towns dedicated to mining or specialized farming (rubber?), but they quickly get abandoned when mine is exhausted or the output is no longer needed.
Soviet Union built quite a few towns in remote northern locations, they were way bigger than feasible for mining - like a general purpose settlement. Guess what, now it's hard to rationalize their existence, but people are stuck there and see it as their home. People aren't very mobile in Russia.
I imagine even when diamond mining is over we're going to pretend that this is just another town that can get jobs on its own and it will be held afloat by redistribution. It's going to be pretty miserable place for sure, I imagine.