I had an Audi A3 2.0 TDI 2009 model last year.
Customer filled up with petrol and drove 3 miles home. He complained that it didn't feel right, then checked his receipt and realised his mistake.

I went to collect it next day, and it wouldn't even start to pull it off his drive and onto my trailer.

To cut a long story short, I tried my best to keep the costs down as he is (still) a friend. I ended up with new HP pump, full set of injectors, and removing the tank for a thorough cleaning. As well as the usual filter change etc. Total bill over £4000.00. Thankfully his insurance paid out for him.

So my experience is yes, sometimes these horror stories are true.

Having said that I have had umpteen misfuels with no problem other than refilling with fresh diesel, change the filters and bleed.

Nick