There are very few good examples imo. While Golota against Tyson seems one, i remember reading somewhere that he did in fact suffer a concussion and they found some abnormality or bleeding/swelling on the brain afterwards. Almost always too harsh to call a top fighter out for quitting, they dont get there with that in them and we arent in there bodies, etc. I think that fighting to survive from the get go actually takes a lot less than doing everything you can to win and then packing it in once youre out of options, and we see that all the time.