MonoBehaviour.OnTriggerExit(Collider)

Description

OnTriggerExit is called when the Collider other has stopped touching the trigger.

This message is sent to the trigger and the collider that touches the trigger. Notes: Trigger events are only sent if one of the colliders also has a rigidbody attached. Trigger events will be sent to disabled MonoBehaviours, to allow enabling Behaviours in response to collisions.

	// Destroy everything that leaves the trigger

	function OnTriggerExit (other : Collider) {
		Destroy(other.gameObject);
	}

using UnityEngine;
using System.Collections;

public class ExampleClass : MonoBehaviour {
    void OnTriggerExit(Collider other) {
        Destroy(other.gameObject);
    }
}

OnTriggerExit can be a co-routine, simply use the yield statement in the function.