#6 Brock Lesnar leaves for UFC

This one is only a matter of time, as Brock Lesnar has been rumoured to be on his way out the door all year. He signed a short-term extension with the WWE prior to WrestleMania 34, hence why he retained against Roman Reigns, but the end of Lesnar's run in WWE is coming.
It's expected Brock will drop the title at some point this summer (likely SummerSlam) and from there, he'll head to UFC. There are already rumblings of a Brock Lesnar vs. Jon Jones super fight for Brock's return to the Octagon. While losing Lesnar's star power may hurt WWE to a certain extent, many fans will be happy to see full-timers on top.
15 shocking wrestling couples - Find out now!
Goldberg ruined Bray Wyatt's career? - Watch now!