Realistically, the Caprice was only a 'demo' model. It never saw a day of duty.
The Impalas are long gone from service according to my sources. I did manage to spot an unmarked Impala in an older video from OnSceneTV (or loudlabs, cant remember which one).
Assuming this project is set in 2017, a lot of older stuff like the 06 Chargers would be replaced too. You'd also lose the MX7000 equipped police units.