I wonder what our "keep" ratio of FA's was compared to the rest of the or how many did we get before they even became FA's? Our drafts at the end couldn't replace what was happening and they weren't very good overall. Definitely not good enough for team that doesn't bring in new FA's very often. But over the course of a decade + there weren't a lot of positions needing a FA signing from some other team either.
Since the instances of free agents who we might call guys who got away in FA over the last decade are so few, I think the first question is answered. All you have to do is look at the players who move around in the league in any one season to get an idea. Here's one list as of April 23 for this past offseason:
http://www.nfl.com/news/story/0ap30...nfl-free-agency-key-trades-freeagent-signings
There's always a position that can be upgraded with a FA, a trade, another high pick if the capital is available. Think about the Packer RB and ILB positions in particualar over the last decade.
Of course there are the other ways a team loses players. Career ending injuries (Collins, Finley, Johnathan Franklin), retirement (Raji), trade (not a Thompson thing), or guys who never fully recoverd from injury to stay on track. A couple guys in this category who stick in my mind, given the ILB struggles over the years, were Desmond Bishop (hamstring surgery) and Sam Barrington (ankle), good players who suffered serious injuries, never fully recovered, released, kicked around the league for a couple of years, and were then out of the league. There are lots of guys who fall in this category, playing then injured than forgotten, with not enough excess physical talent to survive when it is diminished by injury.