I'm not entirely sure specifically which 'holdovers' you're referring to. It could be about holdovers in a job (employees who remain after others have left or a restructuring), or it could be something else entirely. More context would be really helpful.
The Holdovers is not based on a true story. It's a work of imagination crafted by the writer or filmmakers for entertainment purposes. There are no real-life counterparts or events that inspired it directly.
It's hard to say for sure. Sometimes movies claim to be based on true stories but take a lot of liberties. Holdovers could be one of those cases where there's a mix of fact and fiction.