Roman, who ran the 49ers offense over the last four seasons with head coach Jim Harbaugh, will re-join Rex Ryan, who was named Buffalo's new head coach Monday.
San Francisco not fighting to keep Roman does not come as a surprise given the regression of the offense in 2014 that culminated in the "mutual" parting between Harbaugh and the organization. After ranking 13th in the NFL in scoring in 2013, Roman's offense fell back to 25th, scoring 19.1 points per game this season.
Ryan and Roman previously worked together with the Baltimore Ravens for two years. Roman was an offensive assistant while Ryan was defensive coordinator in 2006 and 2007.
Roman became the subject of ire from San Francisco's fan base while the offense floundered, despite the front office adding skill players in the off season to aid in Colin Kaepernick's development.
The 49ers threw more in 2014 than in the previous three seasons, putting the onus on Kaepernick to improve as a passer. But veering away from the physical running game that helped reach the three straight conference title games ultimately played a part in an 8-8 finish, the club's worst record since 2010, the year before Harbaugh was hired.
In joining the Bills, Roman will likely have more autonomy to run the offense than he did in San Francisco, where Harbaugh had veto power on play calling. Roman would relay his call to Harbaugh on the sideline, who would issue the play to Kaepernick. There were many times Harbaugh would overrule Roman's call, but exactly how often has was a mystery during Harbaugh's tight-lipped tenure.
In Buffalo, Roman will be joining a head coach with a defensive background in Ryan, who takes over the NFL's fourth-ranked scoring defense. Ryan is replacing Doug Marrone, who left the team after two seasons where he combined to go 15-17.