Partial Source: Pwinsider
UPDATE x 2: While Batista's return was leaked over the weekend, the plan was to reveal his return on last night's RAW.
WWE's original plan was always to have Batista return at the RAW before the Royal Rumble pay-per-view so that he can appear in that match. Having the announcement run last night is so that the WWE can spike a rating for that episode of RAW, and to create interest in the Rumble PPV.
UPDATE: It was officially announced during the special Christmas-themed edition of WWE RAW on Monday night that former WWE Superstar "The Animal" Batista is indeed making his return to the company in 2014.
WWE announced Batista's return for the January 20th edition of WWE RAW. JBL did voiceover work over the weekend at WWE HQ in Stamford, CT. The company decided to run a vignette after word leaked out. As noted, they weren't happy about it.
ORIGINAL: Batista has been putting on a lot of muscle for his return to WWE. It was previously reported that the plan was for Batista to make a surprise return at the Royal Rumble. One source says that he could win the Rumble and challenge Randy Orton for the WWE World Heavyweight Championship at WrestleMania but that is not confirmed by any means. The deal was set up by Triple H.
Batista isn't getting as good of a deal as Brock Lesnar, but he is getting a very, very good deal. It will include appearances at PPVs, RAW, SmackDown and live events. It's said to be a "close to full time" deal that will keep him in the company past WrestleMania 30.