The Packers defense fell off for two seasons because of massive amounts of injuries to the secondary and linebackers. When they moved Mathews to ILB it was because they went through their first two ILB's at that spot. At one point they were down to the nickel corner as their number one player, and that's not counting their two stud DL who got hurt and suspended. The Packers aren't much of an example for what you're talking about.

If the Broncos don't get a QB they were be relegated to irrelevance for quite some time. That might be worth it to take the time to develop someone.