From my experiance diesel in a gas truck or gas in a diesel doesn't just kill the truck or cost thousands to fix like auto dealers like you to believe. Out of probably a dozen pickups that have had the wrong fuel put in them all I have ever had done was draining the fuel tank of the wrong fuel and refilling with the right fuel. If the mistake was caught after only pumping a few gallons the tank is just filled the rest of the way with the right fuel and kept full for a few 1000 miles to dilute the wrong fuel as much as possible.
I deal with this at least once a summer.