So this was told to me by my brother FuzzyWuffles. He discovered that if you don't choose a defense when you duel a pirate, you can't die from them. At least, he didn't pick one and then he lived. Hope that you find this helpful!
From Fuzzy:
"When I first attacked a guy, I chose scimitar and failed. The next night I attacked another guy, and it showed that I chose scimitar and didn't show anything for him. The player then claimed that he hadn't picked anything and lived."