I think he's weighing up his future, heard a few reports he will retire. Hopefully he'll carry on, and yeah Arsenal keep on being mentioned as well as new york red bulls.He hasn't officially retired has he? I thought there were a few London clubs looking into signing him?
Also, Buffon is only 34 (IIRC), and this season has been one of his best for Juve.. He's got a few years left in him yet. Whereas Del Piero is pushing 40 and is like to command a pretty big wage despite spending more than half the season on the bench. It's probably more of a business decision than a sentimental one by Juve.
From what the Juve board said a few months back, it sounded more like a sentimental reason rather than business, something along the lines of the only Juve player who will always have a place in this club is Buffon. Heard a few times he was willing to take a wage cut, so really not sure why they didn't want to resign him.
As for Del Piero not playing this season, I don't think it was due to footballing reasons, seeing as he played really well and scored some important goals in the very few games he played. Conte just wouldn't ever pick him.