The concept is simple... if a person puts diesel in a gas vehicle, and that person realizes it quickly enough... they simply pull over, syphon out all the diesel and add gasoline in again and the problems should go away.
But if a person puts diesel in a gas vehicle and runs it for awhile, no matter if you syphon out the diesel and put in gasoline... it won't run. The fuel lines, fuel injectors, fuel filters will all need to be changed out. Not to mention that the problems could extend into the engine.