If Chaos could end things wouldn't they have done it already?
Chaos is self defeating, they are near incapable of working together by virtue of their existence and they don't really want to outright destroy the world per say anyway
Tzeentch in particular doesn't want to actually full out win almost any conflict since as the god of schemes, change, evolution and hope he abhors the idea of winning the great game and being stuck with the stasis of victory, he
needs to define himself against some form of adversity to adapt against, usually the other Chaos Gods, actually outright winning and eliminating the opponent is antithetical to his nature
All the Chaos gods have this to some degree, Khorne
needs endless conflict and war, Slaanesh
needs people to experience the emotional extremes of suffering and joy, even Nurgle
needs the people to wallow in stagnation and corruption
Chaos needs the world to sustain itself, if they eat everything then there's nothing left and they die off
So their current goal is to just make it so that the world is one of unending strife, war and suffering to both sustain themselves and to give them a fun toy box to kick around for giggles, and well, by those parameters they've kinda already won; life in the world of Warhammer already is one of constant struggle, horror, violence and suffering
Chaos is also being physically shut out of the world due to measures from the Slann and High Elves, namely the way stone network and the great vortex which act to siphon excess magic out of the world to deny Daemons the ability to just manifest on the material plane, without that Chaos would have a far more active hand in all the events that are transpiring, so I suppose they haven't truly won after all
They all dream of the day they can break through to the mortal world and reshape it in their image eternally