i definitely think it's possible that jax could come back somehow, i know that's mainly cope speaking but like they're able to do a lot more stuff now than before, caine asked if they needed "help with that" (in relation to jax), caine isnt all-knowing so it's entirely possible there's a way to fix abstracted people that he didn't know about, etc. etc. i know abstraction is a suicide metaphor but also in a literal sense the people who have abstracted ARENT actually dead and seem to be in a much happier place by the end than they were at the beginning of the series trapped in the cellar, able to enjoy themselves and be at peace despite their condition. so i think it'd also work well as a metaphor for someone who's struggling incredibly hard to the point that others may consider them a lost cause, but who still have the potential with enough time and effort to keep living.
esp since there's so much emphasis placed on pomni and the others making the fort and making sure everything is as good as it can be for her. she is still there, just sort of separated from everyone, which doesnt really feel like she's died. again, it feels more akin to her being in a really dark place and everyone doing what they can for her until she's well again. (but there being a limit to that and at the end of the day the only person who can "bring her back" is herself) and maybe that will never happen. but it's possible. ik im prioritizing metaphor here over literal canon and its much safer to assume that she's just gone forever but idk i think there's a decent argument for the idea that there's still hope for her