Please keep death duels around, Tom. Surrender duels get abused, true, but people agreeing to death duels are generally serious about it. You can even make it more lethal if you want.
Maybe make it cost money to challenge someone to a duel? You'd have to hire an impartial judge, an arena, etc.
If you just want to RP sparring, have both nobles go to the academy and train together. Sparring equipment costs money and need frequent replacement.