What would happen if one of the dark gods win the great game. Will this cause the winner to disappear due to the lack of chaos in the warp because if they win it will be one constant force?
I geuss all of chaos would lose that chaotic diversity they love so much. Imagine the entire faction becoming giant diseased fat guys!!!
I find this to be a dull question, a BETTER question is: What Chaos God is more likely to beat the other four? But to stay on topic, Chaos would either be incredibly unbearable to have fun with, I'm looking at you Slaanesh *shiver*. Or act like Orks, and scream blood for the blood god all the god damn time. Unless of course Nurlge wins, Nurgle is everyone's dad.
Tzeentch had at one point been the strongest by far for quite some time before the other three joined up to bring him down. As a way to make them all even he broke his staff releasing "magic" across the universe, he is trying to get that staff reassembled(Blue scribes). But this basically outlines why a single chaos god can not win, ever. If one does get far enough ahead the other three will team up to restore the balance they share.
As long as sentient species with complex emotional thought and psychic apple juice inside them exist, none of the gods can just be "defeated". Unless you somehow get rid of some things such as hate, decay, evolution, war, famine, lust, greed, ambition, knowledge, death, growth, anarchy, happiness, sadness, acceptance, blood, pride, insanity, living things, curiosity, and disease. You know, just to name a few.
Pretty much @Daemonkin It's more that Tzeentch is actually able to get them to listen to each other temporarily, as for the magic staff story, how much of that is actually true is up for debate, but in actuality if it comes down to sheer raw strength, it's Khorne