I'd drive it.
In the old days, peeps used to put petrol in with their diesel to stop it going waxy in the winter. So "all weather" diesel must already have something in it to thin it!
The wife and I have both, in the past, accidentally filled the tank in two different vehicles, neither Landies but one was a more modern car with "fly by wire" injection.
The tanks were just drained then filled, and as the pipe from the tank never goes to the bottom, there would always have been some petrol left once they were filled up with diesel. both cars were fine.
If you take it to a garage they will deffo tell you to not only have it drained but also prolly make you do other stuff.
Up to you, but I really wouldn't do that unless driving it gives funny behaviour. But I would keep topping it up with diesel rather than driving till it's nearly empty. So you would be continuously diluting it.
Best of luck