Unity Instantiated Object Script not repeating?

Ok I have well... 2 Questions

my first Question: If I instantiate an object, do the script stay on it, and the script starts like how they were in the beginning of the game.

my second Question: I instantiated my object, but I keep getting this error

UnassignedReferenceException: The variable target of GreenGoUp has not been assigned. You probably need to assign the target variable of the GreenGoUp script in the inspector. GreenGoUp.Update () (at Assets/Resources/Scripts/GreenGoUp.cs:23)

well basically lets say I have Envelopes(which are objects), I thorw my object(which is a prefab) into a trigger, and when it hits the trigger, the object is destroyed... and then I instantiate the object back to its starting position, But if I try to throw my object onto the trigger again. nothing happens.

The thing is I have a script in the maincamera that does a random range and puts it into a variable and depending on the number, a script runs. ill display my script now for one of the Envelopes.

MainCamera Script

using UnityEngine;
using System.Collections;

public class RandomFunction : MonoBehaviour {

    int n;
    public GameObject blueObject= null;
    public GameObject greenObject= null;
    public GameObject yellowObject= null;
    public GameObject redObject= null;
    public GameObject orangeObject= null;
    public GameObject purpleObject= null;

    void Start () 
    {
        n=Random.Range(0,1);

        switch(n)
        {
        case 0:

            greenObject.GetComponent<GreenGoUp> ().enabled = true;
            Debug.Log ("GreenGoUp Should be Working");
            break;
        }
    }
}

Script for one of the envelopes

using UnityEngine;
using System.Collections;

public class GreenEnvelope : MonoBehaviour
{
    bool isMove = false;
    public float speed = 40;
    Vector3 targetPosition;
    Vector3 currentPosition;
    Vector3 directionOfTravel ;
    public Transform target;
    public GameObject playerObject;
    GameObject Green=null;
    //public GameObject playerObject;


    void Start()
    {
        playerObject.GetComponent<OnTrig>().enabled=true;
        Debug.Log ("GreenEnvelope is now on, I should be moving");
    }

    void Update()
    {
        Debug.Log ("GreenEnvelope is now moving");
        targetPosition = target.transform.position; // Get position of object B
        currentPosition = this.transform.position; // Get position of object A
        directionOfTravel = targetPosition - currentPosition;
        if (Vector3.Distance (currentPosition, targetPosition) > .2f) {
            this.transform.Translate (
                (directionOfTravel.x * speed * Time.deltaTime),
                (directionOfTravel.y * speed * Time.deltaTime),
                (directionOfTravel.z * speed * Time.deltaTime),
                Space.World);
            transform.Rotate (new Vector3 (Time.deltaTime * 400, 0, 0));
        } 
        }
}

This script lift the envelope a little so It can be displayed to the user so he can throw it

using UnityEngine;
using System.Collections;

public class GreenGoUp : MonoBehaviour {

    Vector3 targetPosition;
    Vector3 currentPosition;
    Vector3 directionOfTravel;
    public Transform target;

    //public GameObject playerObject;
    public float speed = 40;



    void Start () {
        Debug.Log ("GreenGoUp IS WORKING");
    }


    void Update () {
        Debug.Log ("GreenGoUp IS GOING UP");
        targetPosition = target.transform.position; // Get position of object B
        currentPosition = this.transform.position; // Get position of object A
        directionOfTravel = targetPosition - currentPosition;
        if (Vector3.Distance (currentPosition, targetPosition) > .1f) {
            this.transform.Translate (
                (directionOfTravel.x * speed * Time.deltaTime),
                (directionOfTravel.y * speed * Time.deltaTime),
                (directionOfTravel.z * speed * Time.deltaTime),
                Space.World);
        } 
    }
}

This script is on the Trigger that destroys the object

using UnityEngine;
using System.Collections;

public class OnTrig : MonoBehaviour {

    ParticleSystem particle;
    public GameObject playerObject;
    public GameObject greenDestroy;
    bool isMove=false;
    public GameObject Purple;
    public GameObject Green;
    public GameObject Blue;
    public GameObject Red;
    public GameObject Orange;
    public GameObject Yellow;
    public GameObject mainCamera;



    void OnTriggerEnter(Collider col)
    {
         if(col.gameObject.tag == "Green")
        {
            Destroy(col.gameObject);
            Debug.Log ("GreenEnvelope Has Been Destroyed");
            Green = Instantiate(Resources.Load("Prefabs/greenEnvelope"),new Vector3(-11.63f,-10.49f,30.09f), Quaternion.identity) as GameObject;
            mainCamera.GetComponent<RandomFunction>().enabled=true;

        }
    }
    void OnMouseDown()
    {
        if (Input.GetMouseButtonDown (0)) {
            isMove = true;
        }

        if (isMove == true) {
            playerObject.GetComponent<GreenEnvelope> ().enabled = true;
        }
    }
}