i agree that the effect is marginal, as with that much hp the creature would live for a while anyway. and then theres the mechanic im not following of when a demigod dies it turns into a mortal guy? wheres that coming from?
imo itd be more interesting if the demigod was instead a cheap immortal creature with 1hp and 3ish atk and if/when it dies generate a spark or two or something of that nature.