Getting script to update list of transforms when destination reached or the transform's game object is inactive

So I have some turtles, and currently they find all the game objects tagged "Waypoint", find the closest one, and move towards it. If I add new waypoints it updates to include them which is great. However, if the waypoint they are moving towards becomes inactive they don't stop moving toward it, and once they're at the waypoint they just stop. I tried to create a stopping distance that, once hit, will make them change destination, and also code that changes the destination if the destination object is inactive. Neither are working. Would love some help finding a solution!

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 using UnityEngine.AI;
 
 public class TurtleAI : MonoBehaviour {
 
     public float MoveSpeed = 10f;
     public enum AISTATE {SCUTTLE, HIDE};
     public float HideTime = 10f;
     public AISTATE CurrentState = AISTATE.SCUTTLE;
     public float StoppingDistance = 1f;
     public GameObject FollowObject;
     private NavMeshAgent ThisAgent = null;
     public Transform WaypointTarget = null;
 
     //-----------------------------------------
 
     void Start () 
     {
         FollowObject = this.gameObject.transform.GetChild (0).gameObject;
         ThisAgent = GetComponent<NavMeshAgent> ();
         ChangeState (CurrentState);
         MoveToNearest ();
     }
 
     //-----------------------------------------
 
     void ChangeState(AISTATE NewState)
     {
         StopAllCoroutines ();
         CurrentState = NewState;
         switch(NewState)
         {
         case AISTATE.HIDE:
             StartCoroutine (Hide());
             break;
         case AISTATE.SCUTTLE:
             StartCoroutine (Scuttle());
             break;
         }
     }
 
     //-----------------------------------------
 
     public IEnumerator Scuttle ()
     {
         while (CurrentState == AISTATE.SCUTTLE) 
         {
             if(WaypointTarget!=null)
                 ThisAgent.SetDestination (WaypointTarget.position);
             yield return null;
         }
         yield return null;
     }
 
     //-----------------------------------------
 
     public IEnumerator Hide ()
     {
         transform.position += new Vector3 (0, -20, 0);
         yield return new WaitForSeconds(HideTime);
         transform.position += new Vector3 (0, 20, 0);
         yield return null;
         ChangeState (AISTATE.SCUTTLE);
     }
 
     //-----------------------------------------------
 
     //Sets the nearest waypoint
 
     public void AddWayPoint(Transform WayPoint)
     {
         if (WaypointTarget == null) 
         {
             WaypointTarget = WayPoint;
             return;
         }
 
         //Compare distances
         float CurrentWaypointDistance = Vector3.Distance(transform.position, WaypointTarget.position);
 
         float NewWaypointDistance = Vector3.Distance(transform.position, WayPoint.position);
 
         if(NewWaypointDistance < CurrentWaypointDistance)
             WaypointTarget = WayPoint;
 
         if (CurrentWaypointDistance < StoppingDistance)
         {
             WaypointTarget.gameObject.SetActive (false);
             MoveToNearest ();
         }
 
         if (WayPoint.gameObject.activeInHierarchy == false) 
         {
             MoveToNearest ();
         }
     }
     //------------------------------------------------
 
     //Move to nearest waypoint in scene
     public void MoveToNearest()
     {
         //Move to nearest
         GameObject[] Waypoints = GameObject.FindGameObjectsWithTag("Waypoint");
         foreach(GameObject WP in Waypoints)
             AddWayPoint (WP.transform);
     }
 
     //------------------------------------------------
 
     void OnMouseDown()
     {
         ChangeState (AISTATE.HIDE);
     }
 }