To begin with the Orthodox do not believe that anyone is born to be condemned to hell.  If it is possible for any person to be saved, God will do - and already HAS (in Jesus Christ) done - all that can be done for that to come about.

The Church and its Sacraments or Mysteries are vehicles by which this happens most effectively.  It teaches, preaches and makes the Lord even palpably present here and now to save us.

Those who have not entered it consciously may still be blessed by it in many ways - in part by others who have.  This may be the case with your grandfather - we are all inter-connected.  Clearly he, too, has been a blessing - certainly to you and your family since you have this high regard for him.

The Lord's works are a mystery.  No one is far from Him - He draws near to everyone.  It is He who sustains us, provides for us and guides us along paths where we may unfold to become the god-like beings He intends us to be.

The big question is always one of free will. God does not save those who will not be saved.  When the decisive moment comes - when he stands before the Lord and sees Him as He is, and also sees himself as he is in that holy Presence - will he joyfully go to Him as the One he has, unknowingly, been loving and serving by the way he has lived, or will he, sadly or angrily, depart from that Presence?  And where could he go, since all reality is based and grounded on the One-Who-Is?  The torments of hell are these: to find oneself rejecting that Presence and to have nowhere to hide from it.

It sounds to me like your grandfather is one who WILL accept and rejoice in that Presence.  On the other hand we do not know his mind and his heart fully.  We can hope but certainty lies beyond what we can see and know empirically.  Our response to this uncertainty lies in faith and in prayer.  That is why the Church prays for everyone - including the departed.  We do not know exactly how that prayer works: does it make it easier for a person to prepare for that encounter?  Does it make that encounter easier to bear and embrace?  Does this prayer work forward through time or backwards as well as in the present? 

Time, you must know, is relative.  Einstein gave a scientific basis for that statement.  Those whose perspectives are based upon the Bible have "known" that for millennia.  The time we know best is NOW.  And now is when we turn to the Lord with all things - including our troubles about loved ones who we feel may not be on the way to salvation.  As you do so consistently, humbly, expectantly, I am certain that you will find comfort, hope and peace in your concern for your dear, wonderful grandfather.