He's been serviceable in spurts, and is still an absolute wizard in the faceoff dot; but his speed and strength are completely shot. It's been his hockey IQ carrying him, as he looks exactly like what you'd expect a 38 year old, 5'10 player with a bad back to look like.
If he got a month off and a chance to recover, I think you could squeeze a little more out of him. But the Oil have been running a bare-bones roster this season and he was forced to be an everyday player. Thus that gas tank is completely empty.