The unlocking thing is an over-reaction, there are 2 ways to draw diesel into the fuel pump, either an electric lift pump in the tank, or a smaller transfer pump driven off the main fuel pump. The main fuel pump and transfer pumps are driven off the engine so aren’t a problem until you turn the key. Lift pumps are cheap compared to a whole common rail system.
As for fuel pumps in common rail systems, the cam and follower are separated by about 20 microns of diesel at 2000 bar when operating under full load, gasoline doesn’t have the lubricity necessary and won’t maintain a hydrodynamic layer. Metal on metal contact will lead to surface fatigue pretty quickly and injectors don’t work so well full of debris. A whole cr system will make a lot of cars a write-off pricewise, and people like me are employed to analyse failed parts returned under warranty – we can tell when there’s been lubricity breakdown rather than poor machining etc.
The amount of unleaded you can get away with depends on the lubricity of what it’s diluted with, in future if it was to hypothetically happen again I’d top up with something like vpower diesel not supermarket stuff if possible.