If that station is bringing in decent revenue, then that market has come a long way in the past decade. How many cm units an hour are they running and out of those, how many do you believe are devoid of trade? There's been times in the past where rock would get large numbers, but would be difficult to sell on the street.
A stable sales staff in the present day is the exception, not the rule. If they are billing reasonably well, I'd modify for the betterment of the station if the numbers stink, but I wouldn't completely dump out of the format.
One reason that they would be billing well is that their sister station, Jack-FM is one of the three or four easiest sells in Jackson. A client can buy a schedule on Jack-FM, then for an upsell of several bucks a pop, can get spots on Rock 93.9.