The downside of this activation is that Muzzin has been officially de-activated. With Johnsson on LTIR since his injury in early December, Jake Muzzin has just been sitting on the playing roster as an extra since his injury in late December.
In order to make enough room to re-activate Johnsson, Muzzin is now on LTIR, not merely IR. Even assuming that’s backdated to the date of his injury, we won’t see him back on the Leafs roster until after the horrible bye-week/All-Star Leafs hockey desert is over at the end of this month.
The official word is that Johnsson is a game-time decision, so he might cause the lines to get shifted around a little.