Wave Spawn Script not working? From Null to Destroy Object.

So I have a wave spawner script and an attack script. My waves of enemies only appear for one wave. Once I destroy the enemies they never appear. Is it because I am destroying the game object rather than sending it to null?

Bellow is my wave spawner script and then my attack script.

 public enum SpawnState {SPAWNING, WAITING, COUNTING};

 [System.Serializable]
 public class Wave
 {
     public string name;
     public Transform enemy;
     public int count;
     public float rate;
 }
 public Wave[] waves;
 private int nextWave = 0;

 public Transform[] SpawnPoints;

 public float timeBetweenWaves = 5f;
 private float waveCountdown;

 private float searchCountdown = 1f;
 private SpawnState state = SpawnState.COUNTING;



 // Use this for initialization
 void Start () {
     waveCountdown = timeBetweenWaves;
     
 }
 
 // Update is called once per frame
 void Update () {

     if (state == SpawnState.WAITING) {
         if (!EnemyIsAlive ()) 
         {
             Debug.Log ("WaveCompleted");
         } 
         else 
         {
             return;
         }
     }



     if (waveCountdown <= 0) {
         if (state != SpawnState.SPAWNING) 
         {
             StartCoroutine( SpawnWave (waves[nextWave]));
         }
     } else {
         waveCountdown -= Time.deltaTime; 
     }
 }

 bool EnemyIsAlive()
 {

     searchCountdown -= Time.deltaTime;
     if (searchCountdown <= 0f) {
         searchCountdown = 1f;
         if (GameObject.FindGameObjectsWithTag ("Enemy") == null) {
             return false;
         }
     }
     return true;
 

}

 IEnumerator SpawnWave(Wave _wave)
 {
     Debug.Log("Spawning Wave:" + _wave.name);
     state = SpawnState.SPAWNING;

     for (int i = 0; i < _wave.count; i++) 
     {
         SpawnEnemy (_wave.enemy);
         yield return new WaitForSeconds(1f/_wave.rate);
     }

     state = SpawnState.WAITING;

     yield break;
 }

 void  SpawnEnemy(Transform _enemy)
 {
     
     Transform _sp = SpawnPoints [Random.Range (0, SpawnPoints.Length)];
     Instantiate(_enemy, _sp.position, _sp.rotation);

 }

}

///////////////////////////////////////Attack Script//////////////////////////////////////////////

{

 public GameObject[] MyEnemies;

 //public GameObject[] MyFishes;

 public Animator anim;

 // Use this for initialization
 void Start ()
 {
     anim = GetComponent<Animator> ();
 }
 
 // Update is called once per frame
 void Update ()
 {
     if (Input.GetKeyDown ("w")) {
         MyEnemies = GameObject.FindGameObjectsWithTag ("Enemy");
         //MyFishes = GameObject.FindGameObjectsWithTag ("Fish");

         for (int i = 0; i < MyEnemies.Length; i++)
         DestroyObject (MyEnemies [i]);
         
         //for (int i = 0; i < MyFishes.Length; i++)
         //DestroyObject (MyFishes [i]);
             

         anim.Play ("DaniAttack");
     }
     if (Input.GetKeyDown ("s")) {

         anim.Play ("DaniSheild");
     }

} }