“Just after the climax of the trilogy The Lord of the Rings , Sam Gamgee discovers that his friend Gandalf was not dead (as he thought) but alive.  He cries, “I thought you were dead! But then, I thought I was dead myself! Is everything sad going to come untrue?”  The answer of Christianity to that question is – yes. Everything sad is going to come untrue and it will somehow be greater for having once been broken and lost.”

and…

“The Biblical view of things is resurrection – not a future that is just a consolation for the life we never had but a restoration of the life you always wanted.  This means that every horrible thing that ever happened will not only be undone and repaired but will in some way make the eventual glory and joy even greater.”  Both quotes above from Tim Keller in Reasons for God

and…

“They say of some temporal suffering, “No future bliss can make up for it,” not knowing that Heaven, once attained, will work backwards and turn even that agony into a glory.”  C. S. Lewis

Other than blotting out our memories, this is the only way I can think of, that God could promise to wipe away all tears. That’s what restoration means.