[Tyhm]

Having actually tried some mining, I have the following to say.

1) The rock goes to whoever hit it THE MOST, assuming they are still in the level. If they are not/log off at the last second, then it's freed up. If it's hardcoded to who hit it last, then whoever hits it the most is the only person who can deliver the last hit.
2) The mines should grow...everything on G2K1 should grow and mutate, IMHO. Players should be able to dig into the solid wall with their pickaxes until passageways open up, use boards to reinforce it every 20 tiles, buy lights for the deeper recesses...and to keep it from expanding to the point that all of the underground is opened up into one huge square arena, have timbers rot a week or so after their placed so walls cave in in the less reinforced areas, encouraging narrow, winding paths.

Not easy, but man would that be cool.