In an update on the contract status of current WWE Universal Champion Brock Lesnar, as well as the decision to have Lesnar defeat Reigns at WrestleMania 34, it's being reported by Jeremy Botter (writer for Bleacher Report, CNN, and Houston Chronicle) that Vince McMahon actually made the decision to have Lesnar win during the main event of WrestleMania when he realized that Reigns wasn't getting over with the crowd.
Botter also reports that Lesnar's new WWE contract is only a short-term deal, so that Lesnar could defend the Universal Championship against Reigns at the Greatest Royal Rumble in Saudi Arabia. After that, Lesnar is apparently expected to return to UFC, although he won't be completely gone from WWE either.
Botter posted the following on Twitter:
My understanding is Lesnar signed for one more match. Audible called by Vince during the match last night when Roman wasn’t getting over at all. Now Lesnar will lose the belt in front of a more conducive audience.— Jeremy Botter (@jeremybotter) April 9, 2018
There may be an extra TV appearance in the deal, but at most I’m told this is a two appearance deal.— Jeremy Botter (@jeremybotter) April 9, 2018
Now, it’s likely we’ll see Lesnar in WWE beyond these two appearances. But not for awhile and likely less than we are used to seeing him. He’s committed to putting everything he has into UFC.— Jeremy Botter (@jeremybotter) April 9, 2018
As far as Lesnar and UFC goes: he’s currently targeted to face to DC/Stipe winner at the year-end show in December. I suspect he would be back in WWE for a Mania appearance after that, especially if he wins the heavyweight title. (He won’t win it)— Jeremy Botter (@jeremybotter) April 9, 2018