Changing camera after being destroyed

Hey, I am making a 3rd person shooter game where the main camera is a child of the player game object. I have this so that the camera will move whenever the player moves and will turn whenever the player turns. However, I have been trying to set it up so that when you die, the camera ("MainCamera") will swap to another camera called "GameOverCamera". The reason for this is that because the camera is a child of the player object, when the player gets destroyed, so does the camera and it then displays a black screen saying "Scene is missing a fullscreen camera". Currently this is my script and I don't know how to do this:

 using UnityEngine;
 using UnityEngine.UI;
 
 public class PlayerHealth : MonoBehaviour
 {
     public float m_StartingHealth = 100f;               // The amount of health each tank starts with.
     public Slider m_Slider;                             // The slider to represent how much health the tank currently has.
     public Image m_FillImage;                           // The image component of the slider.
     public Color m_FullHealthColor = Color.green;       // The color the health bar will be when on full health.
     public Color m_ZeroHealthColor = Color.red;         // The color the health bar will be when on no health.
     public GameObject m_ExplosionPrefab;                // A prefab that will be instantiated in Awake, then used whenever the tank dies.
     public Camera mainCamera;
     public Camera gameOverCamera;
 
     private AudioSource m_ExplosionAudio;               // The audio source to play when the tank explodes.
     private ParticleSystem m_ExplosionParticles;        // The particle system the will play when the tank is destroyed.
     private float m_CurrentHealth;                      // How much health the tank currently has.
     private bool m_Dead;                                // Has the tank been reduced beyond zero health yet?
     
 
     private void Awake()
     {
         // Instantiate the explosion prefab and get a reference to the particle system on it.
         m_ExplosionParticles = Instantiate(m_ExplosionPrefab).GetComponent<ParticleSystem>();
 
         // Get a reference to the audio source on the instantiated prefab.
         m_ExplosionAudio = m_ExplosionParticles.GetComponent<AudioSource>();
 
         // Disable the prefab so it can be activated when it's required.
         m_ExplosionParticles.gameObject.SetActive(false);
     }
 
 
     private void OnEnable()
     {
         // When the tank is enabled, reset the tank's health and whether or not it's dead.
         m_CurrentHealth = m_StartingHealth;
         m_Dead = false;
 
         // Update the health slider's value and color.
         SetHealthUI();
     }
 
 
     public void TakeDamage(float amount)
     {
         // Reduce current health by the amount of damage done.
         m_CurrentHealth -= amount;
 
         // Change the UI elements appropriately.
         SetHealthUI();
 
         // If the current health is at or below zero and it has not yet been registered, call OnDeath.
         if (m_CurrentHealth <= 0f && !m_Dead)
         {
 
             mainCamera.enabled = true;
             gameOverCamera.enabled = false;
 
             OnDeath();
         }
 
     }
 
 
     private void SetHealthUI()
     {
         // Set the slider's value appropriately.
         m_Slider.value = m_CurrentHealth;
 
         // Interpolate the color of the bar between the choosen colours based on the current percentage of the starting health.
         m_FillImage.color = Color.Lerp(m_ZeroHealthColor, m_FullHealthColor, m_CurrentHealth / m_StartingHealth);
     }
 
 
     private void OnDeath()
     {
         // Set the flag so that this function is only called once.
         m_Dead = true;
 
         // Move the instantiated explosion prefab to the tank's position and turn it on.
         m_ExplosionParticles.transform.position = transform.position;
         m_ExplosionParticles.gameObject.SetActive(true);
 
         // Play the particle system of the tank exploding.
         m_ExplosionParticles.Play();
 
         // Play the tank explosion sound effect.
         m_ExplosionAudio.Play();
 
         // Turn the tank off.
         gameObject.SetActive(false);
     }
 }

I know it may sound like a stupid question but I really don't know what to do. Thanks.