Gonna go through the list of early game characters, and assess their likelihood of being story relevant again.
Angelina - Low. She has an interesting powerset, but seems to be the exception to the rule that "bigger tits = bigger role". I've speculated that Angelina, among others, might be a success check for when the MC eventually breaks free from H.E.R.O., and she'll likely have a background role in that case. Not main story material imo.
Jess - High. Her former relationship with Jared all but guarantees that she'll make a reappearance. She also has a bunch of variables checking her romance progress. I don't think she's going to be a superhuman, but she will be story relevant again, almost certainly.
Tess - Low to middle. I do not think she'll have the same degree of importance as Jess will, but I can see her entering a relationship proper with Deryl. Plus she is a trio with Alice and Jess, and so while I don't see her being story relevant, I can see her becoming a background character.
Emily - High. All but guaranteed that she's going to be a superhuman, and a powerful one at that. What more is there to say?
Shadow - Stop it. Get some help. She's a old dog that's probably on her last legs as is.
Mia - Middle to high. Regardless of whether you saved Jake or not, the ramifications of what happened with her psyche will need to be addressed at some point. I think the only reason she hasn't made a proper reappearance is because Patreon thinks she's underage b&. So we're waiting on Mia getting an art rework to "age her up". As far as being a main character? Mmmm, might be a stretch.
Tiffany - High. Not much to say.
Claudia - High. Also not much to say here either.
Jared - High. He's gonna walk his walk, but we'll deal with him when the time comes. Probably fuck Jess in front of him too.
Jake - Low. If you've spared him, his mind is broken enough that he likely will not be able to progress past Level 2. He may have bits with Mia, but I don't expect much.
Laurie - Low. Same reason as Jake, can't be too important if she can die, but might have a handful of scenes.
Danica - Low to middle. Danica is a bit weird, cause if I'm not mistaken she does have romance variables, but is a killable character. Makes this hard to judge.
Brianna - High. She's probably going to play a much more significant role when the MC leaves H.E.R.O. and may even act as his in with the police.
Christie - Middle to high. Her connection to the MC and Ella and Emily all but guarantees she'll be important, but its clear superhumanism is not in the cards for her. She can serve alongside Jess as another grounded human perspective.
Demi - Middle to high. Despite being another college girl that hasn't seen much appearance, she is notable for having a game over specifically if you kill her. I think Demi is a character that will become much more relevant later on in the story. Don't sleep on her abilities. There's also the fact that, like Brianna might be the MC's in to the police/government, Demi will probably command his appearance in the eyes of the public.
Clover - Low to middle. Closeness to Demi gives her points, but there's not a whole lot to work with here. Her story seems mostly finished, but I can see her popping up for a sex scene or two.
Jeff - High? Bet you forgot about him, but apparently he and the MC's dad and Aos have been up to shenanigans in the background. Will be nice to learn what that's all about.
Markus - Middle to high. Alice's dad is very interesting. I imagine he's taken over the family in the absence of Alice, but his condition is still a bit of a mystery. I think he might be relevant in the future again.
Nikki - Low. Probably not seeing the femboy from the prison again.
Suicide Wang - Oh god. I killed his ass, but the thought of him appearing again has me shaking. I don't know. It could happen. Maybe just the threat of Wang reappearing again is enough suspense. I don't trust it. I had to kill him.
I believe that's all. Everyone else is either too obvious to mention, or hasn't stood out enough for me to remember.