In the realm of sitcoms I offer "The One That Could Have Been" from "Friends." In this one-hour episode we're shown what life would have been like for the main cast had they made different decisions throughout the series at that point. Ross isn't divorced from his lesbian wife, Carol (the divorce was finalized off-screen before the start of the very first episode) who's cold and inaffectionate due to her repressed lesbianism. Monica is fat (as she was in the show's pre-history) and still a virgin. Joey never got fired from Days of Our Lives and is a celebrity soap star living in his own apartment as he was in a Season 2 story arc. Chandler had the guts to quit his job (as he threatened to do in another early season episode) and works as a freelance writer trying to sell a story to Archie Comics. Phoebe has a job at Meryl-Lynch and is a hard-nailed investment broker (an opportunity she claimed to have at some point in the past, though it was never addressed on screen, part of the story of the episode revolves around her having a heart-attack.) And Rachel never left her groom at the altar (as she did in the series pilot) and is a rich house-wife with a philanderer husband causing her to contemplate an affair with soap-star Joey.
A sitcom, sure, but for fans of the series it's a fun episode. The end result being the gang pretty much ending up as friends hanging out at the coffee house at the end of the episode, more-or-less in the same place as they are in the regular series. (Phoebe has gotten fired from her job, prompting her to calm things down, Rachel seems to have left her husband and joined the gang, Ross has discovered the truth about her life, and Monica and Chandler have hooked up after Chandler offered to help Monica lose her virginity.) The only problem is that Phoebe's story line feels forced, probably because there was no real major character point to focus on with her as there was with the others.