Well, if you don't mind the new guy's wild guessing...
Adolin was bound to delay his fight with Sadeas for a year. The Weeping marks the end of a year; it could be argued in a splitting hairs sense that the delay was therefore honored. I wouldn't buy it, myself, but something more important overrules it.
Remember the difference in rank that Sadeas created between himself and Dalinar. Dalinar is Highprince of War, and can be considered an arm of the state, and definitely Sadeas' superior officer, especially in this frontier - a city that has just been seized by troops under Dalinar's command.
"It's him or me...I will take this from him." Sadeas declares, in the first sentence, his intention to kill Dalinar. The second sentence is essentially a declaration of intent to seize land that is vital to the survival of Alethkar - not just Dalinar. Both of these lines can easily be construed as a confession of high treason. As of that moment, Sadeas' life is utterly forfeit. The only problem is the method that Adolin followed.
As far as the traitor line, I had a few guesses.
Venli comes to mind first, for her apparent extant knowledge of Stormform and its consequences.
Moash seems unlikely, as the diagram was written too early. So does Adolin, for the same reason.
My money? Well, follow the logic here.
Chapter 41: Scars. Excerpt (partial here) from Words of Radiance, Chapter 38, Page 20:
"...but this was only nine of the ten, as one said they would not abandon their arms and flee, but instead entertained great subterfuge at the expense of the other nine."
So. One of the Orders didn't actually drop their Shards at the Recreance. They left the other knights to die - possibly justifying their abandonment as a means of preserving knowledge for the future. This does not mean they remained Radiant, only that they didn't ditch their Blades or Plate. But the question remains, which order?
Again, following the logic, the order that has the least in common with the others. What's the biggest difference between the orders that we know of? Well, nine of the ten had their Heralds drop out of the Oathpact...
This is probably worth starting a new thread over, but my guess is the (notoriously stubborn) Stonewards still exist in some form, and that the name gives a great big clue as far as where they are. Shinovar - which clearly contains people who know a lot more about the Knights Radiant and Surgebinding than anyone else does.
Google says I'm not the first person to think of this, which isn't surprising to me, but that's who I think the Diagram means when it mentions a traitor.