The main reason I'd be tempted to end the fight here is not the risk element per se. The bits of the quest where we're pushed into the danger zone and have to rise to the challenge are the bits I enjoy the most, and hoo boy, did Deadman and Alectai rise to the challenge like preux chevaliers last round. It's more that if this goes to a round two, it somewhat robs our victory this turn of some of its impact if he's able to keep on going? If our last attacks were survivable, it lessens their implied strength.
But on the other hand, the more formidable Hooknails is, the more beating him reflects well on Halla's own strength. And imagining this like it were the episode of an anime for a moment, one can totally imagine the rhythm and pacing of this fight, the smoke clearing, the audience thinking it was over, and then seeing him rising berserk from the crater. Being able to fight a berskergang warrior is definitely on the bucket list too, so that will be amazingly fun.
I think that if we go for Boss Phase II, which looking at the tally I think is highly likely, maybe we should carve him a runestone or use our fire to make him a cool tomb out of molten glass. He was our enemy, but I think if you look at his courage at seeing death starting him in the eyes there and not giving up, he deserves a measure of our respect.