If Hill were to pass Kevin Faulk's rushing record, he would need about 2500 yards on the ground next year. He could probably easily get that in 2 seasons, and may have a chance at the rushing TD record as well, but I'm thinking he will need to stay until his senior season to pass Faulk.
His longevity was helped by being the third-down back for much of his career. He never had to take the beating that an NFL feature back must take.