Placing one finger from his other hand on Mat's chest -- from which his shirt had been torn by the fire -- Xireon shook his head. "There are things much worse than death, Mat. So much worse." From the place his finger had touched, the skin began to blacken, spreading like a plague. Soon it covered a considerable portion of his chest -- the portion where the heart was.
Xireon dropped him to the ground, his body going limp immediately. Mat's body was dead, but the soul, as with any, lived on. And in this case, the soul's time on the material realm was nowhere near complete. His torment had only but begun. Quickly muttering a few syllables and shaping the Force in his mind, the Sith touched the body and performed the embalming spell to preserve it.
Tobal, now emerging from a state of transfixion upon Mat's final moments, had taken off down the sewers. Almost as an afterthought, Xireon waved a hand at him, the flaming rocks from all about the sewer flying into the Jedi at speeds enough to bury themselves into his skin. Like bullets they struck, but the Jedi kept running.
The voice of Xireon Jiren echoed in his mind as he fled. Escape if you will, then, but know that in your soul, you made your choice. You could have stopped him. But it was... convenient, wasn't it? The boy was too dark to be one of you, and so you allowed him to sacrifice himself. You have shown to me your true self, and that is what I desired. Remember my words, Tobal Hadul; you and I are the same, on the inside. The same ancestry flows through our veins: know that you are but one step away from being what you know you can become only in your heart of darkness.
A sadistic laugh, this one real, echoed down the tunnel until it reached Tobal as he left Xireon's sight.