i really liked patrick mckay's answer regarding how arondir survived getting stabbed. it was obviously a reference to arondir's comment in the first episode of the series about how elves heal themselves but it's good to have that actual confirmation and the answer really makes sense within the context of the scene and how it was clearly presented.
like, i get that people have this perception that being stabbed = mortally wounded and that 1v1 = fight to the death but it really doesn't and beyond the stab itself, the scene showcases that arondir was simply hurt. he's injured, that's all. he wasn't dying. hell, the scene quite literally ends with adar kicking arondir directly in the face in order to keep him down before walking off as arondir is shown crawling on the ground so, to me it was pretty clear that adar wasn't actually trying to kill him and that arondir would be alright.
also, i really like that both patrick and ismael (in a previous interview) put an emphasis on this arondir vs adar moment being primarily about arondir losing the fight. that's what this is about, that's what makes this momentous, it's not that he might have died, it's the fact that he actually lost the fight. that arondir, who is shown repeatedly to be an unstopped and unbeatable warrior lost. that adar beat him and that he was able to beat him because arondir became reckless, he wasn't fighting with a level head. for the first time, his emotions literally got the better of him and he lost and could've been killed because of it.