And what does Zon-Kuthon do, when He is betrayed?
Mostly, of course, Zon-Kuthon does what serves Zon-Kuthon's longest purposes of pain, misery, terror, mutilation, woe.
But if there were a tiebreaker between two strategies - if there is some little thing that Zon-Kuthon can do along the way -
Then Dou-Bral, if He had been so betrayed, would have done some last thing He could to work vengeance on His betrayer.
And all that Dou-Bral was, Zon-Kuthon is not.
Nethys is betraying Him? Of course He is. How amusing. No doubt Zon-Kuthon will be the first of many. Let Him go into His vault, then, whispering nothing to the other gods of how Nethys has begun the series of downfalls that will inevitably lead to Their own destruction, perhaps more completely than Zon-Kuthon's mere sealing. Whoever currently thinks they are Nethys's ally will find themselves mistaken; Zon-Kuthon can guess, of course, that Nethys is probably trying to side with fellow gods who also once were mortal, but Nethys being Nethys, the road that has been started down is one from which Nethys is unlikely to be able to turn back.
It is not a certainty, obviously, but the probability is one to gamble on; and a better gamble than the one where Zon-Kuthon announces Nethys's sins, in which case there is not much chance of lasting damage to the world and misery to the gods at all.
He will go into the vault, then, for a time, and say nothing of Nethys's betrayal. Zon-Kuthon has been exiled once before, after all, and it did not last. Evil stays contained less long than one might hope. If Nethys brings enough ruin to the gods, the vault will last even less.
Zon-Kuthon's pieces begin to gather into the vault. They will not slay Him; they need Him to counterbalance Asmodeus yet.