First the whole part where he had no regrets over leaving his son.
I think he did, even if only briefly, and it was a long time ago, (there was definite intense emotion on his face right after he transformed, as he watched the Shadow carry Rumple away). That tree wasn’t fueled by regret when we saw Malcolm climb it, back then it grew pixie dust, which was positive magic, so I have to wonder if Pan spent enough time in his Thinking Tree, wallowing in his regret, that the tree ended up absorbing all that negative energy, which is why the pixie dust flowers died out and the tree now grows vines that strangle people with their own regrets instead. So whatever remorse Pan might have had has left him, and now he just has no conscience left at all.
I think he’s too far gone for them to give him a redemption arc. The way he’s used and abused his family members, abandoning his son, keeping his grandson prisoner in NL for years, locking his son up in Pandora’s Box, and then attempting to kill his great grandson, is unforgivable.
I do wonder though if we might get an, “I’m sorry, laddie,” when Pan transforms back into Malcolm, right before he dies in Rumple’s arms.