If the ending wasn't terrible.
Which it is.
This is in no way a comprehensive list, its a small snapshot of what, in my humble opinion, should have happened. Actual events and things could easily be added.
I should also point out this is what happens if the "Destroy" option did not kill ALL synthetics and left the Mass Relays intact. Citadel Status is destroyed, but when Shepard opened the arms, All the people who had been resisting the Reapers flee to Earth(So most important characters survive, al-jilanhi dies but she helps buy time for other survivors with her death. But Aetheyta lives, Kelly, Bailey, Even the council).
I don't own any of the characters blah blah blah.
Geth and Quarians
Since the geth literally invite the Quarians back(in peace), then up their contribution by building their immune systems back up super quickly, instead of the 60 years they expected, they could be without masks in like 6. Also they could use an embassy, both of them. If you didn't romance either, Tali and Garrus hook up. A scene with them both on Rannoch or Palaven would be good, showing the life they now have.If however you did romance Tali, then obviously you move to Rannoch with her and party down! Have a couple kids, Quarians are mammals.
Is a MUST, especially with Eve, Wrex and Grunt around. They should also build a statue of Shepard and Mordin (maybe not one of Shep, but it would be nice). A renewed Tuchanka would be sweet, in that sort of ancient design we see in that old city. If Wreav is still boss i think another Krogan rebellions is in order. The success largely depending on whether you gave him the cure or not. If they have no leaders they should more or less fall apart. (save Wrex, betray him, kill Mordin, leave Eve to die, Wreav dies anyway). Relations with the Turians and Salarians basically is all up to Mordin, Eve and Wrex, depending on who lives. Grunt should get a girlfriend, Wrex and Eve have a half dozen children and the Council awards the Krogan a vibrant planet on the condition there are no weapons over a certain destructive power there.
Flourish under Primarch Victus, abandoning most conventional ways of doing things and are busy rebuilding Palaven, eliminating scattered Maruaders as they go(things look less positive the less Krogan ground support you got for them). If Garrus is alive he is offered to be a Spectre, which he accepts or denies depending on relationship with Shepard(if relatively ignored he declines, if Shep retires and he was romanced, also declines, if romanced and not retired, he accepts. A shot of Garrus with his family would also be nice (finally get to see a female Turian, although i doubt they differ that much being semi avian and all). If romanced, Shepard and Garrus help restore Palaven and live there(i'm unsure to have children be legitimately made, no, not like that! I mean genetically compatible).
Peacefully coexist with the rest of the galaxy, maybe getting one of their planets back. (Only queen from me1, otherwise they're forced to be put down.)
More or less stay the same, except perhaps an apology to the other races for keeping that beacon a secret. Liara and her father both gain prominent positions in the government, but Liara refuses(seeing as she has another job already) Not sure how this would work exactly, but Samara's daughter Felare restarts the monastery and(if she survives) Samara visits her regularly and (perhaps) retires from being a Justicar. Shiala could be involved somehow, an award for bravery perhaps. Aria (presumably) gets Omega back, dlc about this has been hinted so i'm not sure where to go with that...she drinks her wine and we see the patriarch(if he survived) on her huge arse couch. If Liara was romanced, she and Shepard build a home on Thessia and have 3 blue babies, 2 we see in a scene while we see Liara pregnant with the third.
The Salarians. If Mordin survived, he helps smooth things out between the Krogan and Salarians(although if Wreav is boss, things still get worse despite his efforts). If he cured the genophage and wrex is chief then Maelon comes out of hiding(if he survived) and takes up his professor's mantle and morals, helping the krogan ethically and becoming a lecturer at a Salarian university. Perhaps a shot of him honoring Mordin, maybe at the statue the Krogan put up, as well as him apologizing to Eve. Major Kirrahe ends up running STG(after being promoted, given he survives me1 obviously)
The remnants of the Batarians. If Balak is still alive, then he takes what remains of the fleet and retakes the homeworld, scrapping any and all Reaper technology, possibly with the help of the Alliance (depends) solidifying a peace between the two races as a new government that is a non totalitarian regime like the hegemony before it. Balak grudgingly admits that humans aren't useless and sends Shepard a message of thanks. If Balak is dead then whoever else takes his place does it, but not as effectively.
The Elcor and Volus.
They retake their worlds, nothing major, would like to see a scene of the elcor heavy armaments blasting away husks and the volus bombing fleet actually doing something though.
Hanar and Drell.
The Hanar finally come through with a proper way of preventing Kepral's syndrome(only if medigel upgrade is given to doctor at the hospital). Kolyat ends up working with Feron for liara, but not as an assassin, mostly a contact, bodyguard or a spy (ala kasumi without the kleptomania). If you got and completed the side quest involving Kasumi the Hanar home world manages to hold out until the other fleets of the galaxy show up before they're overwhelmed. If Thane was romanced then Shepard and Kolyat keep in touch and visit each other. A Memorial of Thane is erected in the citadel if he died fighting Kai leng.
Regains the trust of it's colonies and helps rebuild them as much as they can. Also sending special forces to clean out any pockets of resistance that Cerberus or any remaining husks/indoctrinatees may offer. Shepard may or may not be shown here helping depending on a choice(and if he/she survives).
Diana Allers becomes the main spokesperson for Battlespace, getting her own talk show and keeping people updated on where is safe and where isn't, also warning them to stay away from reaper tech and inform the closest alliance vessel(s).(No idea how to include Shepard in here if she was romanced)
Ken and Gabby get married (depending on who you support, if you support Ken, they just date). They still work on the Normandy with Adams, Also adams and Dr Chakwas end up going out, Chakwas also keeps up with her bottles of Serrice Ice Brandy with Shepard each year, toasting the fallen and their victory.
Miranda joins N7 and her sister goes into colony development (if romanced Shepard joins them on a mission, again only if chosen to not retire).
Jacob and Brynn name their baby after Shepard, (hinted at the first name, not any actual dialogue stating the name, more implied) With Jacob being reinstated as a Lieutenant.
Jack remains an instructor at the new Grissom academy, whipping students into shape(if mission is completed and survived suicide mission). If Romanced and a biotic, Shepard joins as another Instructor.
The Archer brothers reunite and Gavin does not ask for forgiveness, but rather, to just be with his brother once again(if they survive, paragon overlord ending).
Hackett retires after all reaper forces are vanquished(Hackitout) and Anderson is given a Hero's funeral, with millions in attendance, Kahlee Sanders touches his coffin, and leaves his dog tags on top, Shepard also attended, thanking him for everything and delivering his eulogy. Vega and ash/kaiden in the background, cue 21 gun salute and hundreds if not thousands of salutes plus a small monument in Anderson's honour. Fade to black while panning up, showing some of the construction of rebuilding earth(with sufficient assets, or it's being rebuilt from the ground up).
Vega follows through with his plans to join N7, and depending on how Shepard treated him, he becomes more paragon or renegade.
Cortez goes back to flying ships, but this time for N7, at the request of Vega and Shepard if he was romanced.
Traynor ends up with an R&D department, but with a bit more of a dangerous edge(weapons testing, etc), she keeps playing chess with Shepard(if played chess against) and the Commander ends up being a match against her and they remain good friends(or get married if romanced by femshep).
Kaiden Or Ashley remain Spectres(if they survive) and get help from Shepard even if he/she retired(only if romanced). Otherwise they remain good friends.
Joker. As far as we know and everything (if you don't want to be spoiled in a minor bit of story, skip this). Both Joker's father and sister are dead, and i think he should visit their graves, with EDI, shed a manly tear or two, and she gives him a hug, concern etched on her face. He continues to pilot the Normandy with Edi riding shotgun and the Normandy becomes the flagship of the Alliance. Eventually, a small breakthrough allows Joker to actually get around with only a minimal risk of breaking his bones. Edi and Joker eventually get married(With Shepard best man or maiden of honor obviously, and hey, its legal somewhere right?) and they adopt some orphans from the war, possibly from Joker's home colony. With the Geth fully sentient and highly productive and peaceful members of the galaxy (and in light of all her help to defeat the Reapers), EDI is given the same rights as a human, as are they.
--------------!!!!SPOILER!!!!----------Okay not really, but whatever.
Or Prothean as it were. If Javik was never encountered, he dies in the stasis pod, Cerberus's meddling ends up damaging the pod too much. If the mission is done however, all good. If encouraged to touch the Memory shard he follows through on his promise, going to find his dead comrades and put them to rest, then he disappears, never to be heard from again, but he makes a small Prothean beacon-type device, which contains everything he knew about his species and any others he knew about, so that the protheans will not be forgotten. If not encouraged however he travels the galaxy, learning what he can and applying his antihero doctrine where he sees fit, eventually a hanar cult develops with him as the main focus, he mostly ignores them and tells them to go away. Liara publishes her book about him, titled "The Lone Prothean: Last of the Ancients"
Shepard's epilogue entry is too huge to “speculate” on, for me. But, based on Romance options and a final choice in which Shepard can decide to retire or not(that is something i reckon should happen).
Obviously with their chosen Love Interest, they live with them, Earth for humans, Thessia for Liara, Rannoch for Tali, Palaven for Garrus. If Thane was Romanced, Shepard spends some time on the Hanar homeworld, and makes sure to properly honour Thane's memory, always remembering him. Specific happenings in the epilogue depend ENTIRELY on choices.
Thank you all Hold the liners who read this far, you're wonderful people.
Hold the line and Hack it out.
A Small snapshop of what ME3's epilogue SHOULD look like.
Blog entry posted by Reaper's Armegeddon, May 16, 2012.