TBH, if you're gonna go as far as disfiguring him you should probably just kill him and make it look like an accident. Like "a shard from the wand got stabbed in his throat, whoops". Sure, his family might want to take revenge but given it's a duel he called and a death (apparently) caused by his own hand they won't be able to do much. Cutting his ear off? Yeah, that ain't getting written off as an accident.
also while I'm at it: IN WHAT KIND OF RETARDED UNIVERSE DO PEOPLE ENGAGE IN DUELS WITHOUT AGREEING ON AT LEAST THE WEAPONS FIRST. Like sure I'm gonna sit here in my tank, let's duel bro it'll be fun.