WATCH: Falcons to receive taste of what could have been in 49ers matchup

Reunion will be the theme of the afternoon when the Atlanta Falcons visit the San Francisco 49ers in Week 15. Not only will the Falcons see Kyle Shanahan for the first time since he left Atlanta at the end of the 2016 season, Atlanta will see former Falcons running back Tevin Coleman as well.

Furthermore, quarterback Matt Ryan will face off against his cousin, 49ers offensive tackle Mike McGlinchey.

But heading into this matchup, one can't help think about the what ifs that exist around the Falcons from the last few years.

49ers head coach Kyle Shanahan served as Falcons offensive coordinator for two years in 2015 and 2016. He was named NFL assistant coach of the year in 2016 when quarterback Matt Ryan won MVP and the Falcons went to the Super Bowl.

The day after blowing a 25-point lead in Super Bowl LI, Shanahan left to become head coach of the 49ers. It took him three years, but he's finally built a winner.

Over those three years, the Falcons have slowly deteriorated. Bad salary cap management, poor drafting, injuries and aging have contributed, but nothing may have led the Atlanta's decline since its Super Bowl appearance more than Shanahan's departure.

No in the Falcons organization can be blamed for Shanahan leaving. It's inevitable that every great assistant coach will eventually leave to become a head coach. Coming off a near Super Bowl win, the Falcons weren't going to depart with Dan Quinn nor pay Shanahan enough to stay another season as offensive coordinator. There's no guarantee that would have worked anyway.

But while the offense has been good and sometimes even great since 2016, it hasn't been elite. The Falcons have been through two offensive coordinators as a result.

Meanwhile in San Francisco, the 49ers offense is excelling under Shanahan, posting the second-most points and rushing yards per game this season. The rushing attack has helped Jimmy Garoppolo grow into his own the last few weeks. In New Orleans last Sunday, Garoppolo threw for 349 yards and four touchdowns. 

Ryan is still playing well but not at an MVP level like with Shanahan. A big reason why is because of the lack of running game and blocking around Ryan, each of which are staples for Shanahan-led teams.

The 49ers defensive unit is also similar to Atlanta's defense from 2016. Speed and pass rush is the key. San Francisco is third in the league in sacks with 45, and the 49ers have nine more interceptions than last year.

In other words, the 49ers have the team the Falcons were -- the team the Dan Quinn envisioned building and was close to crowning with a Super Bowl ring three years ago. 

Now at the end of the decade, it's the type of team the Falcons don't appear anywhere close to being.