Johnson's spot was taken by Chad Simpson, a running back out of Morgan State who played with the Colts in 2008 and 2009. In 25 games with the Colts, Simpson rushed for 147 yards and three touchdowns on 30 carries. He can also contribute on special teams if needed.
The official Redskins depth chart hasn't been updated yet, but Keiland Williams will likely move up to No. 2 behind Clinton Portis, with Simpson taking over as the third-string running back. In two games, Williams has yet to receive a carry, but he does have four receptions for 15 yards.
With Willie Parker's release before the season and now Johnson's departure, the Redskins have gotten younger in the backfield. Parker turns 30 in November, and Johnson turns 31 in November. Now, the Redskins have Portis, who recently turned 29, and two younger backs: Williams (24) and Simpson (25). Johnson and Parker obviously showed their age and have lost a step or two, and although the addition of Simpson doesn't make the Redskins much better, it's productive for the Redskins to have some younger, more flexible backs. Williams can catch the ball out of the backfield and Simpson can do that while also playing special teams. Parker and Johnson basically only carried the ball.
Still, according to the Redskins Insider post linked above, there still may be a slim chance that Johnson returns after this week:
"Asked whether the Redskins plan to re-sign Johnson after this week, [Peter] Schaffer [Johnson's agent] said, 'I don't know. There are no guarantees about anything in this league.'"Isn't that the truth?