The API reports that on average, State Gas tax is 48.8 cents per gallon, and diesel is 54.0 cents per gallon. So, at most, a 5.2 cents per gallon penalty on diesel. Federal tax on diesel is 6 cents per gallon, so the states actually eat a little on diesel taxes, on average. Not really much of a penalty for passenger cars, particularly given the mileage they generally achieve.
Right now diesel is running about 60 cents a gallon higher than gasoline in this area. (It was just shy of a dollar higher in October). It is very likely that gasoline options will reappear in vocations they had lost popularity in. Garbage operations here are now switching to propane, even with the high inital investment, because it is cheaper than running diesel anymore. Given the high cost of the diesel option and tge more complicated systems due to tightening emissions, and it becoming tougher to claim better mileage wipes out the higher fuel cost, yeah, I can see some changing back.