Why do you think the chances of death are too high? It sounds like you are bringing notions of FTO combat with you into this entirely different game.
I actually have a mechanic in the game called Incapability which is a state after making someone’s health go to 0. You are not quite dead, but you’re totally helpless, and you can’t be finished off until at least 24 hours of being in this state. To duel, you could just fight until reaching this state, and then heal them (or let them heal themselves). However, that does run a small risk of inflicting a serious injury, which applies a negative buff to their stats (which could turn permanent if it isn’t healed with high quality medicine and a high knowledge attribute). The chances of inflicting an injury are low though, and even sparring should have its risks, but it definitely isn’t lethal.
This idea is totally able to be done within the current set of features.