The problem is that Thomas and Johnson have similar power running styles. Meaning opposing defenses don't need to adjust to either back.
As a punt and kick returner Johnson isn't a threat to break a long return. He's reliable when it comes to catching the ball, although, the ball that hit off his facemask in Week 3 might have been the single biggest turnover of the season.
With Thomas due back by April's mini-camp the team may decide to add more speed in the backfield.
Adrian Peterson showed well in limited action, but like Thomas and Johnson is considered a power runner.
If the coaching staff trusts Peterson to learn blitz protection, something he struggled with as a rookie, then he could be the backup to Thomas.
The Bears could still acquire a speedier back via free agency or the draft.
Likelihood of Johnson returning: 50-50