Man that sure is an ending.
So it's clear to me that the guy in the truck is Reiji. No other male characters have light hair, and the way Chako talks about him, I can't see him being dead. And the only person Gen told not to wait for him with Reiji, so literally could only be him. Meaning "that woman" is likely Nagi.
I think Reiji's mother finally snapping at him and him getting to yell back at her was the closure he needed to get past the abyss. She was the final thing actually weighing him down and tying him to the town. I feel like this would have been more obvious with even just a few more pages of Ryo's signature "characters looking at things with certain expressions to convey feelings" panels, which we might just get in the tankoban.
They did set up Reiji possibly finding peace in the mountain village where Shino'oka lived, I just didn't expect that plot point to come back after Reiji's continued descent.
Kinda hate that we got a last minute fakeout with Nagi's true name (people keep saying it was Haru, no, that was one of the many fake names she used while living with Mao, which is why her real name was censored in the flashback).
Honestly, this is the ending I was expecting. A cut-away with a flash-forward that only hints at the good ending, almost exactly like how Himegoto ended, complete with a last minute redemption for the guy who was a creep to the protagonist, did a crime, and became a shut-in (Gen in Abyss, Nemoto in Himegoto).
(Also ftr this is only a few years later, not 20 like some folks are assuming. Age-20 release refers to Gen being released now that he's an adult, ie 20 years old, implying he was previously charged as a juvenile.)
Sensei, however, feels completely ignored in the ending, which is odd for her having clearly been an author's favorite. I think I would have liked her abandoning Mao in front of a hospital more, or even just leaving him on a bridge for thematic purposes. Sensei going full Misery on the guy is just a little out of left field.
Also I just gotta say: Yuko being on her death bed up until Esemori died is just weird as hell. She seems pretty fine now??? So it's weird that we're also not really getting a resolution for her either.
All in all: I guess I won't really feel satisfied until I see what gets added for the tankoban so I can make my final thoughts.