The Denver Broncos will most likely utilize their franchise tag on Miller however they should seek to get a long term deal done.
If that doesn't happen the Broncos would have to spend a ton to tag him and they do not have a ton of cap space already (currently $13 million). Miller could be one of the rarer free agents to ever hit the market as he could command a ton of money and attention on the open market.
Here is a list of the teams that need a quality linebacker terribly, the Arizona Cardinals, Kansas City Chiefs, Green Bay Packers, Cincinnati Bengals, Minnesota Vikings, Houston Texans, New Orleans Saints, Detroit Lions, Atlanta Falcons, Dallas Cowboys, San Diego/ Los Angeles Chargers, Baltimore Ravens, Miami Dolphins, Tennessee Titans, Cleveland Browns, New York Jets, Indianapolis Colts, and the Buffalo Bills.
Yes 18 out of the 32 teams in the NFL could use a quality linebacker whether or not it is to compliment one they currently have. This means if Miller hits free agency he is pretty much guaranteed a $100 million contract, there are too many teams willing to pay for what Miller brings to the table. Miller has been with the Broncos since 2011 and has played in 72 out of 80 games in his career. In 2015 Miller played and started in all 16 games this season plus the playoffs.
He had 35 combined tackles, 11 sacks, and 4 forced fumbles in the regular season. In his career with the Broncos he has recorded 260 combined tackles, 60 sacks, 16 forced fumbles, 10 pass defenses, an interception, and a defensive touchdown. Miller's $9,754,000 cap hit is nothing to scoff at either but there are more teams suited to pay for it out there. Miller is only 26 and getting better every season.