Pierre LaFlamme: would retire to teach strategy and/or diplomacy at a military academy under either The Council or - in case The Council eventually succeeds with their revolution - under the new Gallic government.
Henri Croix: would found his own station building and trading company, and retire as it's CEO. (Croix & Co. - Construction & Commerce is the current idea, damn, lot's of C-s...)
Docteur Charles Lavoisier: he already gives lectures and conducts researches, this wouldn't change much. Would conduct on-the-field researches with flying in space occasionally, as long as his health supports it.
Have no idea for Peter Bourne yet. Probably a simple retire as an old man after decades of shipping.
Kohaku would join a band and become a famous guitarist
Lexa will never retire, she's too poor
Kaylynn already retired from the Order and just sits around writing books
Thomas would use that Maths degree of his, probably work for Interspace or some similar corporation.
Magnus would retire again, since he only came out of it to help clean up Bretonia and protect the people because of the war.
Roger would probably join the Colonial government in some way, or have a quiet retirement on Pecos or Yuma.
Susan would probably end up on Yuma helping her father run the colonisation effort there. Liam is never in space anyway.
Michael would probably end up in a bar somewhere, alongside Sam.
Dennis would likely take a desk or storehouse foreman job for IMG, spend more time with his wife Claire and raise their second child when it's born.
Iain I'm not so sure about. He's outlawed in his home of Bretonia, and made a similar name for himself in Rheinland. Might end up living the socialist dream with the Coalition.
Gauss would head out to the Omicrons again, buddy up with the Zoners again.
Alvarez Santiago - [TBH] - Would go back to drinking in the bars on Crete like he was before he came out of retirement.
John "Rorry" Santiago - |RR - That story is well on it's way
Veygaar - Kishiro - An accountant on Planet New Tokyo.
Logan - Reavers - Gun for hire on New York until he is killed in action.
Cain - IC|E - This guy will run convoy escorts till he's to blind to see and goes head first into a corona.
Levesque - Brigands - A local drug dealer on New Paris.
Jim Bo Jenkees - Crazy Pirate/Terrorist - Have an epiphany and turn from his evil ways to become a volunteer at an Old People's Home, spoon feeding grandpas and grandmas their blended veggies.
Jake Dreams - CR| - A teacher to the next generation.