Its not the actual Petrol in Diesel running issue you should worry about:
With modern Diesels (Common Rail) the High Pressure pump produces around 1600 – 2000 bar of pressure, as you can possibly imagine the tolerances within the Pump are minute/very small……. to that end it relies on the quality of Diesel to lubricate the Pumps moving components during operation……… If the Diesel is diluted down (as a result of Petrol contamination) the Lubrication quality is drastically reduced, it isn't now you'll have a problem but the future could get very expensive, worst case is usually new: fuel pump £800, new injectors £600-£800, new fuel pipes & the actual time for someone to do it…………
BMW say in the event of a Customer putting Petrol in a Diesel and the vehicle is run you should replaced all these as a minimum to ensure the Warranty is still valid, cost is about £4000….. Ouch