Chaos is more about a never ending cycle, we don't really know where it begins but it ends in Nurgle and is manipulated by Tzneetch throughout. What's in the cycle? Violence mostly, but Chaos has no desire to end. Chaos isn't about annihilation (with vast dominating empires being the exception, as Chaos despises hegomonies) it's about persistence.
The two perceptions of "Eternal" and "Change" of Chaos isn't necessarily far off from the reality. However, as the Chaos Gods ultimately want dominion over the universe, only Tzeentch truly prevents his game from ending. As a whole however, if Chaos were to overpower the other factions, the Warp and reality would become one tumultuous ever shifting roil of pure emotion. There would be no semblance of rational thought or order: emotion, much less the warp it impacts has no physical laws that dictate what it can and cannot do. In essence Chaos and Necrons stand at polar opposites and yet they are so far apart they join the circle just shy of the same place we "began" it. It's like a Pac Man game where you walk off one side of the screen and end up on the other side because of the common denominator of the ultimate fate of each faction's total Victory is a zero sum and infinity. If either faction wins, the galaxy is doomed to utter destruction. This is why: Chaos: The Warp is the stuff of Change. Dictated by pure unadulterated emotion to the point of madness and incomprehension it is the beating heart and the soul of the galaxy. Summoning demons as Chaos inevitability does, weakens the barrier between real space and the immaterium. Demons and warp energies tear apart reality, bringing the realms of Chaos closer to overtaking the universe. If this would ever to occur, the universe would be awash in the stuff of chaos. Reality would cease to exist and only the twisting netherworld of the non-physical, non ordered, nonsensical world would remain. Even then, without Order (the psychical universe, beings to feel emotion, ect.) for change act upon, Chaos ceases to work. Once unleashed unchecked, it will eventually run out of fuel; leaving the universe in a formless unrecognizable oblivion. Necrons: Oldcrons: Hellbent on the extermination of all life caused by their self loathing towards their frail mortal bodies and mindless pact with the C'tan to make way for: Newcrons: Hellbent on the extermination of all other life in their sentient march to reforge their Empire and transfer their souls into perfect living bodies to enjoy a peaceful eternity with. Outcome: the galaxy is wiped clean in order to make room for the resurgent Empire. Should the Necron's succeed, all other life except that chosen by the Necrons will be obliterated / erased from existence by the very nature of their weapons. It is quite literally a racially motivated, genocidal holocaust of all life deemed unworthy by the Necrotyr; which is everything - such genetic perfection cannot be achieved by such an Ayran race with so much self loathing of living flesh and love of immortality. Ultimately, the pariah of the race, the Silent King, is the only one that truly has the unobtainable end goal of attempting to achieve both; what he doesn't realize in his guilt ridden state is that he cannot have both: the moment his bargain was struck and the first Red Harvest began sealed the fate of the entire galaxy to be condemned to oblivion in his vain search for every mortal's dying wish: resurrection.
Except for the fact that there are entire systems, planets, and societies in the warp. Life persists in the Immaterium, albeit being mutated and changed by exposure to the raw power of the gods. It's highly dangerous of course, but your summation that Chaos is an unarguable destruction of all life is simply erroneous. A possibility perhaps, but to presume that anything in the realm of Chaos is assured is a grave mistake.
But we're talking ultimate in terms of even when the Gods themselves change because the anchor of belief; set in reality, is absorbed and torn apart by its complete victory will leave nothing but change as a constant. Here, read this: http://en.wikipedia.org/wiki/Law_and_Chaos And we're also missing the point of trying to discuss the personality of each faction.
