As I say it would be a very serious, and dangerous situation.
As I recall Bgile, the first time you mention only part of the country was occupied, not all of it; yes Russia can deploy overwhelming force but would it be 100% effective or would a guerilla war ensue - remember that the USSR tried overwhelming force in Afghanistan, and it ultimately ended in failure and ignominous withdrawal. What could NATO do - well, make the situation very uncomfortable for the Russians, not by offering direct military opposition, but by economic sanctions, other diplomatic pressure and encouraging/arming Georgian resistance. But it would be a very dangerous situation - particulary if Ukraine was drawn into the conflict in support of Georgia.
''Give me a Ping and one Ping only'' - Sean Connery.