The Falcons themselves never displayed all that much interest in guard Evan Mathis, but fans certainly did. He's now off the market.
Teams seemed oddly reluctant to meet the man's asking price, given his obvious talent and production. I have to think his outspoken nature and advancing age were big factors there, but the rumored asking price for a long time was around $3.5 million, and Mathis did finally exceed it with Denver. The Broncos have a dire offensive line situation that makes even the Falcons look somewhat stable.
Let's get this out of the way: Yes, I believe Evan Mathis would have been an upgrade for Atlanta in 2015. I don't see how you can avoid that conclusion, and I'm not entirely sure why the Falcons weren't interested. All we can do now that Mathis is officially off the market is hope that James Stone, Chris Chester, Mike Person, Jon Asamoah, and anyone else mixing in at guard can play well enough to keep the offense running smoothly.