This question is impossible to answer except in hindsight. When someone dies, there is a temptation to think the result might have been different if they had just stayed in the car or had just managed to get out of the car. Calling 9-1-1 when your vehicle first stalls has helped some people survive. The best thing is to avoid this situation, by turning around if a road is flooded. Better yet, avoid driving in heavy rainfall, since sometimes visibility is so poor, it is hard to see that a road is flooded.