I don't think it matters who they sell too because WB will still retain the IP. It might factor in the price if they want to give temp licenses to the buyer but it's not that big a deal in the short term and certainly wouldn't be broad or all encompassing.
As for job losses, I don't think we can say much in that regard other than jobs would likely go in all situations.
This isn't true.
We can say that AT&T seems to be (based off the TweakTown article) wanting to go the Disney route and are looking for an exclusive licensing partner, if that article is accurate - which I see no reason to doubt right now as it makes sense. So yes, if they are looking for an exclusive partner for video game development it absolutely matters who they sell to - they will want someone who can cover all their bases. Licensing agreements, as mentioned earlier, come with definitions of what platforms games are to be developed for, etc.
Warner Brothers Games currently has a large mobile presence that makes a lot of money - I have no doubt that would be included in the deal as well. It would make little sense to get "out" of the video game industry but keep mobile developers just cause, especially when you are trying to maximize sale value and minimize your overhead.
We also CAN also safely say that WB Games staying under AT&T would likely result in fewer job losses, see Matt's posts for more details, but the amount of people employed by WB Games in distribution, production, marketing, publishing, etc is extremely high and all those jobs WOULD be lost if WB Games was bought by another publisher. AT&T may downsize WB Games if they decide to keep them, but they would still need people filling those roles vs. those roles being lost entirely.