Avatar 2: big evil mining company returns to pandora and bombs the shit out of the planet from orbit getting rid of the pesky natives. Wholesale mining of the planet begins
Avatar 3: mining continues
Avatar 4: mining continues until no more unobtainium left, move onto the next planet
"I say we take off and nuke the entire site from orbit, it's the only way to be sure. "
Whoops sorry wrong movie.
But yep in a real world situtation orbital bombardment might be the solution. But then just come up with some phoney science that in order to be effective from orbit the bombs would have an effect on the materiels being mined renderding them worthless.