Update:
The report has been leaked from PWI's Elite section and mentions that WWE wanted to do Batista vs. Daniel Bryan for the WWE World Heavyweight Title at June's Payback pay-per-view but Batista turned it down. Batista felt that losing to Bryan a smaller wrestler after tapping at WrestleMania XXX would make him look weak, especially since he is about to appear in a major summer movie.
So, ultimately Batista decided the time was right for him to leave as WWE has nothing for him as this time.
There is currently no word on when he will be back.
Source
People could hate on him for this, but it makes perfect sense from a character standpoint.
Batista has a reputation among the majority of the WWE fanbase as an animal/monster/badass. He's the guy who should kick the ass of most of the guys he faces. He should only lose regularly (in-kayfabe) to the top guys in the business. Bryan, meanwhile, is a hugely-over, but still largely unproven commodity in the main event scene. He's scrappy, but he's an underdog. He's beaten Cena, Orton, HHH, and forced Batista to submit once, but that was always his resilience and his unwillingness to lose that made that happen (much like Jericho and HBK). But, for the protection of Batista's character, it would be a little silly to have this guy who, whether anybody here thinks so or not, still has a badass reputation among most of the crowd, for him to lose in such quick succession to the same guy.
Now, if he goes away and comes back after Summerslam? Then, if he faces WWEWHC Bryan for the title and loses, it makes more sense. By that point, Bryan's defended the title against HHH, Kane, Orton (most likely), maybe Bray Wyatt or someone else who's worthy. It doesn't hurt Batista's character to lose to him (again) then.
wk