Here are my 1000-1 predictions for how Quaritch will be resurrected:
The Spirit Guide: The cut dream hunt scene showed that the Navi have and engage in rituals involving hallucinogenic substances to try to form some level of precognition or as a magic the gathering player might say scry

So I doubt it would be a big jump that Jake or some other character might undergo such a ritual and via Eywa have several "guides", Grace Augustine as the "good" guide and Quaritch as the "devil/evil" guide.
Eywa's Battle AI: Eywa's ability to "control" creatures with no apparent direct link might indicate Eywa has a WIFI connection of sorts, what if that connection could be utilized to save the memories and personalities of not only all the fallen Na'vi but all humans who perished in the battle (including Quaritch). That would be a formidable database of current military technology and tactics that Eywa could leverage in the next human incursion? Moreover, Quartich could be Eywa's representation for the militarized knowledge/personality.
Either way we are a few years out, and I reckon its a bit early to raise the pitchforks, I have full trust and faith in Mr. Cameron to come up with a twist that totally floors us.