Must Zombie Wolverine or Daredevil roll the extra dice from a hero's roll-on-6 ability when the hits already clear the zone?

Question

Accepted Answer

Yes, as written. The roll-on-6 ability has no 'may' qualifier, so the extra dice are rolled even when the hits already clear the zone. A minority argues that with no other targets left the extra roll should not happen, but it cites no rule.

Marvel Zombies: A Zombicide Game

Must Zombie Wolverine or Daredevil roll the extra dice from a hero's roll-on-6 ability when the hits already clear the zone?