Had a look at that spell.... I see it uses a PermanentDeath GameModifier. Which doesn't kill them (rather seems to sop them resurrecting if they are killed). However it's also got the StealSpirit modifier. Did a quick test and added the StealSpirit to my "KillChampion" test spell and sure enough it kills the bugger dead.
with due respect, I think you are wrong at this one. When I performed my tests the strategic spell killed the champion instantly.