Tuned S55's have been known to have issue with crank hub which throws off timing. I don't think it's happened too much with stock motors, especially with the M2 Comp getting the lowest output variant of the tune. Faults and failures happen, you get it fixed and move on. It sucks when it happens to you but as long as the dealer puts everything back together properly, you should be fine. If they can't fix it, then you hope they do the right thing and buy it back.

Unless he has a good lawyer that won't happen and lemon law lawyers don't take cases that are not slam dunks. There are lemon law rules that BMW will just hide behind and they will fight tooth and nail not to buy an M Car back. He is better off just driving the car or selling it. If he has another engine failure he should start playing the lottery.