There will be a need by 2017 for an OLB regardless of when Matthews might hit the wall.
Peppers is year-to-year; Perry and Jones will be FAs after 2016 while not having demonstrated to date that they have the right stuff to take over a 3-down/70% snap role.
Except for a very few elite rookies, edge rushers require a year of grooming. It's fairly common to see 1st. round edge rushers play they're rookie years in pass down rotation. Then if all goes well he graduates to 3-down play in year 2. It's fairly rare to see an edge-rush rookie walk into the NFL as a well-rounded and productive 3-down player.
If Peppers hits the wall (or just calls it quits), while Perry and Jones just show what they've shown to date in 2016, all reasonably plausible outcomes, we may be wishing the Packers had gone high in 2016 for an OLB by this time next season.
That said, it's hard to see how the Packers could go OLB on day 1 of the draft with more immediate needs. And there's always the temptation to wait and see if either Perry or Jones shows enough in 2016 to take over that spot on a 3-down basis. Perry had the late season surge and Jones will be going into his second year at the position. Over recent years, the Packers have shown a fair amount of wishful developmental thinking at positions of current need.
Day 1 is lining up for D-Line and ILB as the priorities, not necessarily in that order. I think the odds are at least even that we'd see the Packers go OT/G swing man vs. OLB in the 2nd. round, securing a guy they think can graduate to starting OG in 2016. The fact that 4 of the top 6 OLs will be FAs after this season, 2 of them the starting OGs, argues for some action now.
With OLB there's at least the wishful thinking with Perry and Jones for 2017. The most you can say about the O-Line backups is a projection of Tretter at OG, but he has a lot more value in the league at center in free agency.