It is implied that the Buffalo branch is the most stable of the branches that fell under Jan's jurisdiction as the Stamford branch closed, and the Scranton and Albany branches are headed by Michael Scott and Craig, respectively.
Most or all of the Buffalo staff were present during Company Picnic. There, the staff was distraught to learn that their branch was to be closed. The news was inappropriately leaked by Michael and Holly during their picnic skit, before the official announcement was made.
The branch was closed due to the economy by Season 6.