When Hairston comes back the Reds will have to send down a position player. It should be Patterson, or Hopper, or maybe even Valentin (although he's the only decent lefty pinch hitter). It should not be Janish.
The Reds need to build on their young players. Janish is a good defender with decent on base skills who can build on these and become a defensive backup at shortstop, also playing second or third when needed. The Reds are a subpar defensive team and he has value in late innings, when a ground ball pitcher is throwing, or when an infielder is out.
In the minor leagues, Janish showed patience at the plate and hit decently during a couple of seasons. Obviously he is not an offensive threat, but he serves other purposes on the team. I also feel the team coming together around young players and demoting Janish will hurt that chemistry.
Look to the future. Keep Janish.