Respawn enemy tool

Hello,

I have been trying to figure out a way to make this respawn enemy tool be able to start respawning the mob after I killed them in game! It calculates the starting number in game and a max count at the same time, but I can't figure a way to set that respawned obj to a false state after it is killed. Can someone help me?

Code (csharp):

1.  
2. using System;
3. using UnityEngine;
4. using System.Collections.Generic;
5. using Random = UnityEngine.Random;
6.  
7. //vai representar um range min e max entre 02 valores estipulados
8. [Serializable]
9. public class Range
10. {
11.     public float min;
12.     public float max;
13.     public Range ()
14.     {
15.         min = 0;
16.         max = 0;
17.     }
18.     public Range (float a, float b)
19.     {
20.         min = a;
21.         max = b;
22.     }
23.     public float getValueInRange()
24.     {
25.         return Random.Range(min, max);
26.     }
27. }
28.  
29.  
30. public class SpawnArea : MonoBehaviour {
31.  
32.     public Spawnable _prefab;
33.     public Collider _area;
34.     public Collider _ground;
35.     public int _initialCount = 5;
36.     public int _maxCount = 10;
37.     public Range _spawnTime = new Range(10, 60);
38.  
39.     private mob enemy;
40.  
41.     private List<Spawnable> _unused = new List<Spawnable>();
42.     private List<Spawnable> _used = new List<Spawnable>();
43.     [SerializeField]private float _timeUntilNextSpawn;
44.  
45.     // Use this for initialization
46.     void Start ()
47.     {
48.  
49.        //Create our inicial list of spawnables
50.         for (int i=0; i < _maxCount; i++)
51.         {
52.             Spawnable spawnable = Instantiate(_prefab);
53.             spawnable._area = this;
54.             spawnable.transform.parent = this.transform;
55.             spawnable.gameObject.SetActive(false);
56.             _unused.Add(spawnable);
57.         }
58.  
59.         //Spawn the inital number of spawnables
60.         for (int i=0; i < _initialCount; i++)
61.         {
62.             SpawnMob();
63.         }
64.  
65.         //Initialize the spawn timer
66.         _timeUntilNextSpawn = _spawnTime.getValueInRange();
67.     }
68.    
69.     // Update is called once per frame
70.     void Update ()
71.     {
72.         //Update the spawntime
73.         _timeUntilNextSpawn -= Time.deltaTime;
74.         if (_timeUntilNextSpawn <= 0)
75.         {
76.             SpawnMob();
77.             _timeUntilNextSpawn = _spawnTime.getValueInRange();
78.         }
79.  
80.         if (_prefab.GetComponent<mob>().health <= 0)
81.         {
82.             Debug.Log("SPAWNANDO");
83.             Instantiate(_prefab).gameObject.SetActive(false);
84.             _used.Remove(_prefab);
85.             _unused.Add(_prefab);
86.         }
87.     }
88.  
89.     //"Create" a new spawnable by moving one of the unused spawnables into the used list
90.     public void SpawnMob()
91.     {
92.         if (_unused.Count > 0)
93.         {
94.             //Get the first unused spawnable
95.             Spawnable spawnable = _unused[0];
96.             _unused.RemoveAt(0);
97.             _used.Add (spawnable);
98.  
99.             //Activate this spawnable
100.             GameObject obj = spawnable.gameObject;
101.             obj.SetActive(true);
102.  
103.             //Generate a random position within the spawn area
104.             Vector3 pos = MathUtils.PointInsideArea(_area);
105.             pos = MathUtils.SnapToTheGround(pos, _ground);
106.             obj.transform.position = pos;
107.  
108.             //Make the spawnable look in a random orientation
109.             Vector3 lookPos = pos + Random.insideUnitSphere;
110.             lookPos.y = pos.y;
111.             obj.transform.LookAt(lookPos, Vector3.up);
112.  
113.             //call spawn on the spawnable
114.             spawnable.Spawn();
115.         }
116.     }
117.