It wouldn’t be terribly difficult for a reunion of The Office to take place.
Many of the characters we have come to know and love over the years went their separate ways during the finale (Andy went to work at Cornell University, Stanley retired, Jim and Pam moved to Austin, Texas, etc.) but the return of Michael Scott during the finale to take on best man duties at Dwight Schrute’s wedding proved that The Office characters definitely will stayed in each other’s lives.
A reunion could simply pick up a few years after the premiere of the “documentary” based on their lives.
Although the series finale very clearly closed the door on the events of the series, it certainly left a window open for these individuals to possibly come together again at some point.