Sure, the retreat over the single bridge was messy, and even predictable, but, apparently, the more important strategic objective for N. was cutting off enemy pursuit. If you haven't already, read the GA bulletin of Oct. 20. This is N.'s take on what happened. Remember, N. was a genius (especially in his own mind) and he saw his plan for the retreat from Leipzig as genius that was only thwarted by this dummy of an engineering officer.
It doesn't take much imagination to see that if the bridge was only blown at the last second -filled with Allied cavalry and soldiers- not only stopping cold the Allied pursuit but delivering a blow to that army, it would be at least portrayed by N. as a victory in print if not in fact.