[Warning: spoiler-heavy] I have to say the exact same thing occurred to me at the end of the movie. "And so the aliens returned to their dying world." ...yeah,

[Warning: spoiler-heavy] I have to say the exact same thing occurred to me at the end of the movie. "And so the aliens returned to their dying world." ...yeah, to get more ammo. Of course, the counter-argument might be that the Na'vi managed to defeat a heavily-armed base using a skeleton force, before most of the tribes had even turned up, so by the time they got back Pandora could be too well-prepared to resist for them to be successful. Kinetic bombardment is all very well, but you need to get down to the surface to pick the stuff up -- unless you completely destroy every living thing on the planet, in which case you develop a very serious logistical problem (they were growing their own food on the surface).