If the target unit declares a Flee reaction, or gets destroyed for any reason, the charging unit now has a choice: it can either attempt to complete the charge against the now-fleeing (or destroyed) unit, or try to redirect its charge by making a Leadership test. If the test is failed, the charging unit must attempt to complete the charge against its original target. If the test is passed, however, the charging unit can declare a fresh charge against another viable target (the charged unit may declare a charge reaction as normal).

If this second unit also flees, you can instead choose to charge the original fleeing unit. If there are no other suitable targets to charge, a charging unit cannot redirect. Each unit can only make one redirect per turn.