@Snork
I'm feeling tempted to carry out the burning ritual more than just sparing him instead.

Mr. Urobuchi is a talented writer, but he can be incredibly sadistic with his characters. Besides, I think the full credit goes to Magica Quartet for creating Sayaka (and the entire franchise as a whole). Gen just did more as the writer.
Then again, I'm probably just being influenced by a certain concept about what to do with stories with sad/bad ends that I read from Komari's route in the Little Busters! VN...