the ellimist exists outside of time, so doing so would not take away his powers, however could he? i mean, he moved the earth out of the way of the crayak, which was risky, and implied he wouldnt be able to simply bring the planet back if he destroyed it. also, it would most likely be outside the rules of their game, and even if it wasnt, crayak would then do everything in his power to destroy it again, probably in a more violent way, and the elimmist doesnt want to put his people through that.