It depends on whtether they would be given the chase or not.
If not, then leaving close range would be sufficient imho.
If yes, I ask them to roll a competitive Athletics check with their pursuers, modified of course by all appropriate factors (terrain, encumbrance, fatigue, etc.), and using the lowest stats in the group. I also usually use a tracker (5 or 10 counters depending), and every success beyond the other party's roll moves the counter along. Every 3 steps is an event. If the pcs reach it, they can roleplay something like diverting attention of the pursuers or taking a shortcut, and add some negative dice to their pursuers roll. If the pursuers reach the event, they can shoot with a ranged weapon or effect a charge.
Spending fatigue on the fleeing or pursuing rolls allow rerolls of the dice pool.
At the end of the tracker is the result of the chase, either the PC's make it out or they don't…