I don't mind keeping Mantha until someone else wants him, but he needs to earn his spot on the line-up if he wants to actually play. I'm not a big fan of having kids sit while healthy and it makes very little difference to me if it's Mantha or Aube-Kubel who is on popcorn duty. Just make fair decisions that you can back. If he's training well while someone struggles, it's only fair to give him a shot and see if he has found his motivation. Just don't pencil him on to the line-up for 50+ games just because he has a high salary.