2. Cremation would leave options open when it comes to magic, given all the fire deities out there. And...I wouldn't swear to it, but weren't the words used to animate a golem (in the Jewish tradition) written in ashes on the golem's forehead? I can see stretching that idea to somehow infuse a golem with a dead hero's powers.
I'd say have Green Lanterns dump the bodies into a black hole or a pulsar, so that it's impossible to get hold of any remains.