Look on the bright side of the injury - it will give you a bit of time to have a good look at the depth players you have in that position.
So by the time the playoffs roll round you might actually be better off in terms of knowledge about your squad depth.
Haggans looks to be another difference maker you have in the LB core - but I think you have enough quality in that area to cover for him in his absence.
We already know what we have behind Haggans in Harrison, we won't miss a beat. He played last year quite a bit when Haggans was out with a broken hand. Our depth last year was unveiled to us. No mysteries for us except for maybe at Guard and Tackle.