Marlon Byrd has agreed to a two-year deal with the Phillies, so he's not coming back. It's not yet clear how much he'll make there. I wouldn't have minded the Pirates signing him to a two-year deal, but I can see why they would want to be careful about it, given Byrd's age, the fact that they have reasonable alternatives in Jose Tabata and Andrew Lambo, and the fact that Gregory Polanco is on the way. Byrd will likely be remembered fondly in Pittsburgh -- he hit tons of line drives in his brief time with the Pirates, and provided a helpful power bat for their playoff run.
The Phillies were one of a number of teams on the lookout for outfielders, and they wanted a righty in particular, so it's no surprise they would sign Byrd.
UPDATE: Byrd will get two years and $16 million, which is reasonable for the Phillies. A bunch of people on Twitter are making fun of the Phillies right now, which I usually endorse, but I think this is really just the way the market dictates things will go. I can see why the Pirates might have wanted to allocate resources elsewhere, though. Keith Law has a good post pointing out the flaws in Byrd's game, and I have to admit, I didn't have a very clear view of them, since he hit so well with the Pirates. His BABIP in 2013 was a very high .353, and that will likely come down dramatically next year. Add in his age, and that's a problem. Steamer has him posting an 0.6 WAR next season; if that happens, the Phillies won't be thrilled about it.
UPDATE 2:38: The Pirates evidently did not even offer Byrd a contract, despite at least one report that they planned to try to keep him.