As an avid Eagles fan, I have always seen the Eagles running attack to be somewhat thin. This year however, the Eagles will be able to put up some big run numbers with the maturation of Correll Buckhalter. Staley will have to run his freakin' ass off. Buckhalter is young, strong and has incredible moves. I think Staley will need to post MVP numbers to hold his starting job.
I don't think you will see Staley replaced, however, the Eagles may go to a running back by committee if they aren't getting the production out of Staley. As long as he posts decent numbers, I wouldn't expect him to lose his starting job unless he gets injured. If he does get injured, then its up for grabs.
the eagles certainly have gone to a "Running Back by Committee" approach, its work great for the team, but its hell on fantasy league owners