WWE adopts a much stricter regulation on high spots, even greater than they did years later following the Benoit tragedy (and the plethora of injuries around the same time). TNA and ROH differentiate themselves even further with their products, which stood out as they were, and WWE's product takes a steeper dive in quality, both as a result of a top star's absence and as they panic (from PR issues and a scramble to fix the shows).
Brock never goes to UFC, obviously, and I think UFC takes longer to get as phenomenally massive as it does (as Brock was a major draw), but only by a year or so. Brock's return is also a major tipping point for WWE booking after the PG turn (the unofficial start of relying on older stars returning for paydays), so if that doesn't happen then the ME looks very different. Maybe they pull the trigger on Punk getting the WM main? Maybe they're less likely to jerk the crowd around with Bryan?