Damn, the confirmation from Mara that the plan always had been for Thjazi to escape. Mara was meant to be in the Tenebral Reaches and Thjazi was meant to escape, and it was only because she wasn't that Thjazi realised he had to let the execution take place and let himself be killed.
He said, "Not you, anyone but you" when he saw Azune was the Arcane Marshal assigned to scan him, so he realised what position this would put him in. He knew Azune would immediately be arrested if he escaped. But - he only realised he had to actually die when he saw Mara. So there were a few minutes in there - standing on that stage, joking around with his brother over their lunch plans - that he was fully prepared to snap the glyph and put Azune in the noose instead.
So don't worry, Azune! Thjazi didn't let himself be killed just to save you! He was ready for you to die in his place from the moment he realised it was going to be you doing the scan!
