Sounds like you're pinning a healthbar to an enemy and hoping that hitting the enemy, the healthbar will automatically reduce... am I right?
Every enemy instance, create an instance variable called healthbarUID or something.
When pinning the healthbar, store the healthbar's UID in he enemy instance variable healthbarUID.
Then whenever an enemy is hit, also pick the healthbar from healthbarUID and reduce it.
Same method for destroying. When you're destroying the enemy, pick the healthbar with that UID and destroy it first, then destroy the enemy.