Would this apply in the final round also? If it is a rule it would have to. I can see it now. Driver A gets to the final round in Pomona needing to win the race to take the championship. He gets to the finals and his opponent goes up in smoke. Driver A goes through the lights, blows a tire, then makes a right turn into the wall. Sorry (insert favorite driver name here), you lost that race and the championship because you hit the wall after the race was over.
Once they cross the finish line the race is over. The winner then moves on to the next race in the event. I know it may be semantics, but last weekend in Topeka was an event with a series of races to determine a winner, not "a race". In any other form of motorsports, once you cross the finish line it doesn't matter what happens on the other side. I've seen multi-car crashes after the finsh-line in other forms of racing but the results did not change because of the crash. Proffesional drag racing is an acceleration contest. Whoever gets to the finish line first(legally) wins.
Since the final is the last race the rule would not apply. It's all theory anyway. NHRA probably isn't going to change anything.