Life support is already significantly more expensive than a lot of the automated mining equipment we already have, working underground.

Maintenance is a concern, but lots of places are researching human-like robots, which would ideally be capable of performing most simple maintenance items (tightening a hydraulic hose, replacing a worn pin in a joint) - major maintenance would most probably not occur, machines would be a little over designed, run-to-distruction in a year or two and then just replaced....

There's also little sense in making the thing that brings back the goods, also bring back the mining machines, as this additional weight is definitely not the same value as the goods.