Quite awesome to see such a spectacle, though I hope no one got seriously injured and the damage done to the enviroment isn't too high.
If discovered early enough, it could be relatively simple to push a large asteroid off its collision course.
IT. IS. A. GAME.*geez* Its supposed to be fun, which includes a friendly and helpful community of players.
Repulsion force to change asteroid's trajectory by a few centimeters ≠ asteroid being nuked. It's totally plausible if detected early enough.