Meh, it could have a small blast radius, or it could be a one use per game "apocalypse" class spell, or have catastrophic reprecussions on the user for invoking such a spell of chaos and destruction....
It could also make for a good cinematic, but then people would wonder who cast it, and if they find out who, how it would be obtainable. This would make players be either very excited or dissapointed, depending on whether or not you can unlock the spell.
Also another thought, it could be the way one of the demigods or old god gets wiped off the face of the planet when they are defeated. A giant fire and brimstone explosion, or other massive/spectacular scene, such as giant rays of light coming down to save an angelic hero, that would end up the demigod/old god/hero being removed from the battlefield.
Man I keep getting new ideas about the game from each paragraph I write
but one other death cinematic or animation I could think of would be for Regulus, the fallen angel assassin, but when he dies, angels would swoop back down from heaven to carry him back to where he belongs.