This happened about 2 years ago at COS when UA stopped flying mainline flights there and it became an all-UX station. I believe that SkyWest, one of the UX carriers that serves COS, also provides the ground staff.

Service was downright awful for a couple of months...I recall one especially painful IRROPS about a month after SkyWest took over when it seemed nobody that had been there more than a week was working...but eventually the staff figured out what they were doing and now there is no noticeable difference (to me, anyway) in service vs. what I get at a UA operated station.