Sorry, the only reason Seinfeld would go off the air would be if Jerry or other cast members lost the interest or desire to go on with it. Seinfeld is NBC's highest rated show, and something like #3 for the year in the Neilsen's, not #96, and challenging Bakersfield, P.D. for the worst ratings on TV today.
It may be in top 3 but last season's big slip in the creative/writing quality of the show was quite noticeable.
No matter how many times the CastleRock producers may deny the fact but 'Seinfeld's producers have sold out the idea of a cool, hip, urban show with a Wednesday night cult-like following in favor of a typical mass-appeal ready-for-general-consumption NBC's Thursday night sitcoms...
Take Kramer character for instance : mysterious, unconventional, funky character during early days of the show has steadily become a typical f**** sitcom goof just like Bull on Night Court or Christopher Lloyd's character on Taxi or Don Mills' character on 'Three's Company'. Kramer is fast becoming a boogie man with a severe case of shakes and the only thing he's able to say thesedays is his trademark 'Oooo-aaa'....
I give 'Seinfeld' another year or two at most....It'll die from lack uncreativity because when you start streamlining the storylines like the writers and producers are currenly doing now the cool ideas for new episodes just won't be there...If you think that I'm not making any sense, just rewatch last season's finale wich will air next week(9/15) and you'll see my point loud and clear. How lame of a season ending was that?!