it depends on how much diesel you're talking about.

when i worked for a rental car company this used to happen all the time. if it was just a little, a lot of premium could get you through it. however, in most cases the tanks needed to be drained, lines and injectors needed to be cleaned. if someone kept trying to crank it forever the head would have to be pulled, oil and bearings changed in the bottom...but that was very rare.

i still don't understand how people make that mistake. if the correct nozzle is on the pump it won't even fit (it's supposed to be larger). even if it isn't the pump is dirty because of the diesel and usually not connected to a gasoline pump (usually standing by itself). you would think when someone doesn't have to push a button to select which fuel that would send a warning message to the brain.