There is one thing for sure....There would be a lot of younger Captains-folks in the 30s-40s range.
Acccording to Steve Long's Dominion War Sourcebook-Starfleet lost 55% of the Fleet in the Dominion War....that is a lot of senior personnel. So you would see commanders younger than average; For example my Captain in my fan-fiction is just 40 or so-he graduated in 2366-here is his bio below:
CAPTAIN DAVID THOMPSON–COMMANDING OFFICER-USS LUMUMBA species- Human Male (Black)- Born at McKinley Station in the year 2340 to Mychal & Lila Thompson-father is a crew superintendent at the shipyards & mother is a schoolteacher. Was always interested in Starfleet but entered the Academy late in life (age 23) after 7 years as a Merchant Marine crewman & pilot. Found that war gaming & tactics were his forte along with being a helmsman.
Graduated in 2366 after only 3 years b/c of his standing as an MM-served aboard USS Magsaysay during the Cardassian War as a junior Tac officer & head of Stellar Cartography then after the war returned to the Academy to teach for a year then was assigned to Admiral LeBethin’s staff at Starfleet Tactical then went to Deep Space 6; Got his second ship tour aboard USS KRUNG THEP as tac then as acting XO –Has been promoted meritously 3 times in his career for “services rendered”.
Returned to teach shipboard tactics at the Academy in 2370;he left there in 2373 to become Tactical officer onboard the USS KHE SAHN. During that time he was forced to take command of the ship due to the Captain’s infection by the Ciona parasite-the XO having been injured by the Captain and was credited with the defeat of 2 Galor class starships during this time.
During the war he forged a reputation as a daring and unorthodox tactical officer- a factor noticed by many in Starfleet; as such the Khe Sahn and her crew became one of the most successful ships in terms of damage to the enemy.
Considered because of his easygoing nature a more relaxed Captain than most (along with Cdr. Mithora) and has in a very short time developed a close relationship with the crew of the Lumumba but make no mistake. He CAN be an officer if need be.
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And here is the XO of my ship.....COMMANDER CHELA MITHORA Executive Officer- USS LUMUMBA - species Selelvian female- Born on Selelvia in the year 2350 to Jonas & Mitchella Mithora.
Excelled at a early age in every subject & had an opportunity to enter the Daystrom Institute but decided to enter Starfleet Academy & did so at age 14 in 2364 (Selevians mature much faster than many other races in the galaxy).
Was an outstanding student in the Academy as well but chose a rather unusual field of study.
Most Selevians go into the Sciences, not Security or Command but every command that has had her has written outstanding fitness reports on Lt. Cdr. Mithora. Graduated in 2368 & was assigned to Security School Command were she graduated 3rd in her 40 person class overall with a 1st overall in tactics.
Her 1st assignment was as an Ensign in security on the USS CANBERRA where she got her reputation as a no nonsense SO by tracking a murderer on an away mission in less than 48 hours. She was merit promoted by Captain Samisen to the rank of Ltj.g.
Within 15 months she was reassigned to Earth as a Starfleet Internal Affairs officer with the rank of full lieutenant Worked several major investigations for IA & was rewarded with the Federation Meritorious Service Medal, the Federation Medal of Merit & 31 commendations for outstanding service.
But she missed starship service & requested a transfer to " Any ship who will have me as a security officer." She got her wish when she was assigned as a plank owner on the KHE SAHN in 2373 & remained aboard until 2377 when she returned to SSC as one of the Senior Instructors. She taught there until Captain Thompson requested her as XO for the Lumumba.
She-like her Captain- knows every member of the crew is very outgoing in relaxed company but is all business when the job requires her to be & is known as a brilliant interrogator as well as a terrific leader. She has an excellent singing voice & is a tremendous practical joker.
You would have , I think, a more wary Starfleet-it would not forget its primary mission but it would be on a more military/defense basis than before-as noted by the above bios....Remember the period of time -in a 15 year period you had the Borg-the 1st Cardassian War-the Klingon War when Gowron voided the Khitomer accords as well as tensions on the Romulan borders;
Then the Dominion War hit on top of that....Starfleet would undergo SIGNIFICANT changes in their outlook as would the Federation. Yes the Federation would be what it is but with changes.
I would expect Cardassia to be like Germany post WWII expect for the fact there would most likely not be an E. or W. Cardassia.
I would, however , expect the Cardassian Union as we know it to shrink; they could NOT hold the areas they had before due to the devaststation of Cardassia. So I would expect contractions of the DMZ with Starfleet handling the resettlement and other issues.
I was born in a camp on Bajor- I joined the Resistance at 12 to fight for my people and my freedom. I joined Starfleet to help KEEP that freedom. As the Prophets will it I shall not fail you, Captain.
Lt.Commander Varin Rel-Former Starfleet Special Operatons officer-now assigned to the USS LUMUMBA-NCC-78245 as CTO.