I think there could be 3 things that could happen as a result of Ryan going down.
#1. Oren Burks will get plenty of reps with the #1's on defense and may get the call to start when preseason games start, if he shows enough, and ends up as a suitable replacement.
#2. Burks "flashes", but not enough to feel comfy having him as a starter in Week 1 against CHI, so they move CMIII to ILB part-time to share snaps with Burks w/ the caveat that the trio of Fackrell/Beigel/Odom show enough at OLB that Pettine feels OK with giving Matthews snaps at ILB. (All three of F-B-O have been working hard and making a positive impression so far).
#3. Packers feel they have to bite the bullet and go out an sign a veteran ILB (ex: like Bowman) or they bring in another veteran edge OLB (ex: like Barwin, or John Simon.......if INDY releases him)
What I don't doubt is that there will not be any roster additions at either ILB/OLB for at least 2 weeks.........unless there's another injury.