People fight wars over resourves all the time. If the unobtanium is that valuable humans will be back. Especially if their planet is dying as it was said at the end.
I was talking about the attitude of the aliens not the actual fight. A race that was essentially tribal would have been far more caustious when dealing with such a technological threat.
The bomb ship was taken out by grenades yes it was the deus ex machine that gave the na'vi the victory. And that was triggered by their God in the machine (oh not machine trees).