Here are a list of people who will probably appear in the final episode ever. (note: this is pretty much unconfirmed, just like all the "final episode rumors", but Jerry hasn't denied the guest star list, like he did with the "L.A. last episode" or the "Chapel last episode") :
Jerry Seinfeld (Jerry Seinfeld) Julia Louis-Dreyfus (Elaine Marie Benes) Jason Alexander (George Costanza) Michael Richards (Cosmo Kramer) Estelle Harris (Estelle Costanza) Jerry Stiller (Frank Costanza) Wayne Knight (Newman) Liz Sheridan (Helen Seinfeld) Barney Martin (Morty Seinfeld) Danny Woodburn (Mickey Abbott) Larry Thomas (The Soup Nazi) Patrick Warburton (David Puddy) Len Lesser (Uncle Leo) Frances Bay (Mable Choate) Keith Hernandez (Himself) Larry David (probably as a walk-on)