Andrew
there is no definative answer to your question. There are so many factors.
Have a read of this
Misfueling and you can see that depending on vehicle, age, milage, and so on depends on the final outcome.
The key is, that diesel is a lubricant and as such is essential to lubricate all the pumps and injectors. Petrol is a solvent and strips any lubrication off the surfaces it comes into contact with.