You're probably wondering what would happen if Evey actually fell from that high. They'd survive but it wouldn't be pretty. They'd probably be unable to heal from it. But the Mallet would keep them alive. They'd still be able to function as StarHammer, however. It's an effect of the bond between it and Evey. It's a kind of an emergency thing.
Evey's not immortal. And this emergency thing doesn't currently extend to Danae, though it has in the past. You will have a better idea of how this works when we show other wielders. Remember, the Mallet isn't the only weapon of its kind.