#4 No Austin-McMahon feud
The greatest feud in wrestling history would never have happened. There is a fair argument to suggest that there also would have been no Montreal Screwjob had Austin retired following Summerslam 1997.
McMahon had no other future main-eventers lined up after Austin and likely would have had no other choice other than to keep Bret Hart on the payroll. Which would mean, not only would we have no Austin, the Mr. McMahon character would have no impetus for being created either.
No Austin vs. McMahon means no beer truck, no bedpan, no zamboni and no other hugely memorable moments that thrilled WWF fans in 1998-99. What could the WWF have possibly produced that could top that in terms of entertainment value significantly enough to still win the ratings war with WCW?
It is unlikely that Austin would have remained in a non-wrestling role as his character really didn't suit being an authority figure (though he did play one, when his career really did end in 2003) or a manager or commentator. Austin most likely would have stayed at home.