Like a super event that until destroyed continues to create new enemies periodically?
In theory it should be simple...
I'm sure Blizzard incorporated a script call that will check to see if the enemy is alive or dead. Find out if there is one. If there is, then use that call script under a parallel process condition that starts a timer when the enemy dies. Wait so many seconds and reset the enemy's location and revive him there with the call script command. You would need a switch for the hive and a second page for your monsters. When you destroy the hive, let the switch change the monster's pages so they stop coming back to life.