If they trade him, they need to get quite a bit of quality in return. A much better than Oswalt haul. He is signed for two more years IIRC, relatively cheap, pretty durable, and has been pretty damn solid for a few years (not to mention the last 12-month ERA stat).
It seems like most people around baseball, even a lot of Astros fans, act like he is just a relatively common, mid-rotation arm. That's my impression at least. If that is all the value the Astros will get in return, then I hope they keep him.