Calling a function after game over to retry

I have this function i want to call which puts the player back to the menu after all their lives run out. Only thing is I need help calling it inside my function onGUI which shows my game over screen. I want to call the function WaitAndDie if you could help thank you

 function OnGUI(){
 
 if (playerLives == 0 && player == null){
         GUI.Box(Rect(0,0,Screen.width, Screen.height), "Game Over");
         spawner.GetComponent(Enemy_Spawn).isON = false;
 
     
     }
 
 }
 
 function WaitAndDie() {
     yield WaitForSeconds(4);
     Application.LoadLevel ("Menu");
 }