I'm sorry to hear of your grief. Be glad, however, that you possess the Love of God inside of you that you are able to show your love for him! This says much about you.
Powerful Lord, God, Almighty . . . it is your will that we are in agreement with. We ask for nothing that would be outside of your Holy will. And if it is in your will, we ask that you would carry this grandfather of Joshlovesjesus, and place him into the Right Hand of Jesus. We ask that you would lift the Curse of Adam and Eve, and Purify his soul of all corruption. We humbly ask that your Grace, which is sufficient for you, would be extended to this man who has struggled against his will, and that his "sleep" and "slumber" would be alleviated.
Awaken his soul, Lord! We ask that you would show yourself to him, whether he is "in" the body, or out of his body. You are all Powerful and you alone are able to redeem his soul, even if he comes to a point of no longer seeming to "be here" with us. We Trust the Almighty Power that raised Jesus from the dead, and we place that same Trust in the redemption of Josh's beloved grandfather. We ask that you would save his grandfather outside of any good work, or deed, and redeem him based upon your Holy Promises alone. We know that you can do this, for you have done it for many of us. We pray this Prayer in the Name of your Holy and Powerful Son, Jesus . . . Amen.