Petrol in diesel?

If it was a "We must evacuate the area" situation I would say drive it. However, in this instance I would say to pump out the tank of fuel. Store it in a couple fuel containers. Then refill with clean diesel. Now as you run the vehicle add maybe 2 liters of the mixed fuel to every tank of diesel. That will dilute it enough that the petrol won't cause an issue in the engine. That issue is that the petrol acts as a solvent without any lubrication and modern diesel is already bad enough at lubricating the fuel system. To add to that the petrol will also alter the flash point of the diesel and in a newer engine with computer controls and sensors that will cause problems. However, you won't lose the fuel if you slowly add it back in over time.