Lots of agencies, when they approved auto pistols way back when, allowed officers who didn't want to switch to keep their revolvers.
(Most of the agencies around here switched between 1987-1989. Some of them had allowed auto pistols as an option before that, but in most cases anybody hired after the transition period had to carry a pistol.
We had a couple senior (older) guys carrying the issue revolver right up until they made them switch to a G17. I know of one who got so pissed off that he went to the county as a baliff and kept the revovler.