Deirdre might retire to her home continuum, or maybe she and Rebecca would return to Rebecca's version of 2020's Earth. Now that I'm thinking about it, I could see her retiring to a different sci-fi continuum and working as an engineer or cook or nameless redshirt on a spaceship.

Rebecca might go back to her version of Earth, but she might try living in Middle-earth or Star Trek or another universe she likes that she's read about or watched. If she went back to Earth, she would still lead an adventurous life. She might join a rock band or work for a historical reenactment group or something. She would probably go to college at some point. If she didn't find a partner or get married, she would be the awesome nerdy aunt to her siblings' kids.

Boadicea might go back to Terraria and deal with being a terrible person. She would definitely try to go to various different continua first. I could also see her settling down in one of the D&D worlds.

I'm still dragging my feet over My Immortal, but I think the Aviator and Zeb will retire after that—one Legendary is plenty, thank you very much, and at this point they've more than had their fill. They're tired, they've been through a lot, and at this point they're ready to be done with their lives as agents.

They've got a kid to look out for now, too, and since Zeb is more or less Elanor's other parental figure at this point, they'll negotiate another permanent use of the D.O.R.K.S. for Zeb. They retire to a peaceful time period of Gallifrey where Elanor can attend the Academy, and the Aviator and Zeb will remain on-call in case the PPC ever has need of them.

And, at some point many years down the line, Elanor like as not becomes an agent herself.

Oshimo gets into the PPC to research a method to beauty (the reasons will be revealed later in the spin-off; not giving anything away here), so she won't retire until she achieves that.

For real, I don't think anyone told Nume that was an option, but he wouldn't take it anyway. You'll have to pry his RA out of his cold, dead hands. Or maybe force him onto a nice Federation planet within tourism distance of Vulcan. He wouldn't grumble about that too much.

Ilraen, on the other hand, wants a life that includes a family life at some point. (In-universe it's possible this has already happened, but I've shot all developments in the foot by insisting on getting through "Subjugation" first, and we all know how that's working out.) He'd love to finish out his years in his home universe, but failing that, he'd settle for some remote corner of the Uncharted Territories (Farscape universe). Farah and Kkukttak could come, too!

Derik and Gall may relocate to New Caledonia if/when the times comes that they can't keep up with the Suvians. Neither of them would be happy returning to their home universe (or each other's). Gall would prefer to end up a KIA, though—hero's death; Valhalla; bury her bones and Fellrazer's at sea. Derik might say the same (without the Valhalla part), but if he makes it to old age with his remaining sanity intact, he'll return to his Harper roots and become an entertainer and/or teacher to keep busy.

Jenni will at some point go back to her home universe, but since she's immortal it won't be retirement so much as the next phase of existence. And even then she might drop by sometimes to see how things are going with her friends' grandkids and so forth. {= ) Ex-PPCers are welcome in her universe, too, provided they don't try to be main characters and won't be weird about the whole "technically a goddess" thing. Oh, and if her siblings show up, don't listen to a word they say; they're jerks and she left them to play their stupid games by themselves for a reason. (At least, that's my current understanding of the situation. {= P )

Agent Neshomeh will never retire; she'll slowly become one with the Archives, perhaps converting her neural engrams into a Miss Minutes-esque cat hologram that pops up to answer questions, correct the spelling in agents' mission logs, and occasionally knock things off your console when you're not looking. ^_^

~Neshomeh

Charlie would likely go back to their campaign variant of the Forgotten Realms setting as a lich, if they ever were convinced to retire (which would be fairly easy with the right negotiator). The Out of the Abyss module they were in would be long over by the time they went back, so no one would remember them, and any stories they told of the strange realms they’ve visited would probably be brushed off as just a funny lich quirk. They’d find a nice little gothic manor to hide out in, fill it with undead servants, and then just sit around entertaining people in nearby towns and having a fun eternity trying to convenience the tavern-goers that they’re a perfectly normal tabaxi bard (and being comically bad at it).

Jiwon would probably just go back to see the family, provided memory wiping can be avoided - losing memories seems a logical fear for an immortal, and Jiwon’s a nervous type by nature. Explaining what the job experience was like after all this time would be an awkward time, though. Also, going off of a Years Hence ficlet I've had on the backburner for a while, Jiwon would also have to explain why she's a she.

And then there’s everyone else I've written for this setting, who’ll probably never voluntarily retire within the century: Ocotillo, Matterhorn, Dr. Glocktopus, Tess, and the Curator, all for a variety of reasons ranging from simple immortality (Glock) to dedication for archiving all - and absolutely all - of the setting’s history (Curator) to just feeling like there’s nothing left for them to go back to and nowhere new to go they’d find purpose (the others).

Carlisle would probably like to hide away in a library full of old books and no other people; and Mina would probably want to help with the Nursery.

--Ls

• Sergio and Nikki... already did. They went back to the world of their fanfiction of origin, since it is now standing on its own. Sergio became a racing car driver, Nikki started working at and eventually bought out a café. And they had a kid!
• Corolla I don't see retiring in the foreseeable future, since she loves being a technician at DoSAT. She would probably end up freeloading at Sergio and Nikki's house if she is forced to, and eventually find some kind of tech-related job.
• Arumi... I guess she literally can't. Being basically like KITT from Knight Rider, she needs regular checkups at DoSAT. Regardless, she's been an agent since 1998 and she's still sane and happy, so I guess she really likes it there.
• Ditto for Emily. Being a Kancolle ship girl, she has certain "maintenance requirements" that would be very difficult to meet outside the Kancolle continuum (where she cannot return) or the PPC.
• For Syaoron I haven't really fleshed out his PPC backstory much, but I think he would be a bit of on-and-off actually. Work at the PPC a few years, retire on some universe and try to live a normal life for a while, figure out that place isn't for him and go back to the PPC, rinse and repeat.

Going fast-forward a few years...

• Keiko is only working part-time, but as implied by her character arc in the TWWA timeline the PPC is only one of the many things she's trying after giving up on being a racing driver. It won't work out like all the other things, and as per TWWA she was already considering resigning after around one year.
• Shiro and Saki would likely last more than her, but they would eventually retire similarly to Sergio and Nikki. I mean, they're alternates of them... I never fleshed them out enough to decide what they would do afterwards, though.

And now the alternate timeline!

• In TWWA Hajime wasn't thinking about resigning yet when she met Keiko during the Unravell around 2035 HST her timeline, but she would eventually do - to her, the PPC is basically training and experience she's getting for when she will become a Strike Dove operative. As such, she will likely retire no later than 2037 HST when she turns 18 and so is old enough to start some actual work there.

Kaguya and Momoka would just go back to their world ('Guya has a clan to inherit and university education to finish). Helena and Sheen would go back to Pixie Hollow. Urato, Inasuke and Fáelán have nowhere to return to so maybe they'll just stay.