How to spawn a new prefab when the last one was destroyed??

UNITY 2D C#

I have a script. When my player is alive, the enemy manager counts down the time and then creates an opponent.

I would like the EnemyManager to respawn a new opponent, but only when the last one is destroyed. So, if the created opponent (being a prefab) dies, EnemyManager should start counting the time again and if a certain number of time passes, he should generate another opponent.

Any help?

My script:

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 
 public class SpawnManagerWithTime : MonoBehaviour
 {
     public GameObject[] prefab;
     public PlayerBehaviour behaviourscript;
     
     public float minTime;
     public float maxTime;
 
     float time = 0f;
     private float spawnTime;
 
     private int randomPrefabs;
 
 
     void Start () 
     {
         spawnTime = Random.Range(minTime, maxTime);
         randomPrefabs = Random.Range (0,2);
     }
 
     void Update()
     {
         time += Time.deltaTime;
 
         //Check if its the right time to spawn the object
         if(!behaviourscript.dead & time >= spawnTime ){
 
             Instantiate(prefab[randomPrefabs], transform.position, Quaternion.identity);
 
             time = 0f;
 
         }
     }
 }