Watch that fumble again, there is one giant common theme that seems to occur in his running style that I've noticed over the last three years...he does this dumb little spin move and blindly slams his back into the line of scrimmage. I've commented on this before, how I can't believe a 220 pound running back adopts a running move/style of Barry Sanders. It may of worked for Baryy Sanders, but it's not going to work for your average power back.
Here's the good news...he only fumbled...he wasn't paralyzed or knocked into Aruba before his unconcious body hit the ground (see Baltimore playoff game).
Now this is why I don't think you'll see him again as a starter/lead runner...you can't tell me the coaches haven't demanded him to stop running like that. I imagine they sit down with him and discuss his running style. I imagine there are certain fumbles they can live with, but I can't see them living with a guy who doesn't play the way he is coached. And I can't see any running back coach allowing his runner to turn his back to the line of scrimmage where he can't actually see who is trying to tackle him, or how easliy it is to knock/punch the ball out. This is a fundlemental problem - when you are being taught fundlementals and ignore them you end up on the bench.
And another thing...the guy wears pajamas to work...the one's with the feet in them...footsie pajamas.... a full bodysuit, footsie pajama, with a teddy bear hood. I'm serious, he does that. He tries to sell them to the other players. That can't make Belichick feel all warm and fuzzy inside.