Otherwise, morale rules are useless if there is not a fast and fun way to resolve a chase when the monsters break off the encounter.
BX, 1e etc have % Evasion numbers that work fine.
With 3e-4e if the pursuer is as fast or faster then you roll a few Endurance and/or Stealth type rolls. If the pursuee is faster then they always get away, perhaps after a parting shot or two.