I am not at all sure what the Great Cloud of Witnesses or the Communion of Saints fully entails. I do not believe that one can know in this life. But I believe this: Christ trampled down death by death, and with Himself he has (and will) raise all the dead. I also believe that a mere thing such as death cannot make someone who was always in the life of Christ and the Church to be less than with Christ and the Church. He became all that we are so that we may become all that He is: and that includes our experience with death. Such is the Good News of Easter, of Resurrection.
Here is the passage that years ago began my thoughts on this subject:
"How they do live on, those giants of our childhood, and how well they manage to take even death in their stride because although death can put an end to them right enough, it can never put an end to our relationship with them. Wherever or however else they may have come to life since, it is beyond a doubt that they live still in us. Memory is more than a looking back to a time that is no longer; it is a looking out into another kind of time altogether where everything that ever was continues not just to be, but to grow and change with the life that is within us still. The people we loved. The people who loved us. The people who, for good or ill, taught us things. Dead and gone though they may be, as we come to understand them in new ways, it is as though they come to understand us--and through them we come to understand ourselves--in new ways too. Who knows what "the communion of saints" means, but surely it means more than just that we are all of us haunted by ghosts because they are not ghosts, these people we once knew, not just echoes of voices that have years since ceased to speak, but saints in the sense that through them something of the power and richness of life itself not only touched us once long ago, but continues to touch us. They have their own business to get on with now, I assume--"increasing in knowledge and love of Thee," says the Book of Common Prayer, and moving from "strength to strength," which sounds like business enough for anybody--and one imagines all of us on this shore fading for them as they journey ahead toward whatever new shore may await them; but it as if they carry something of us on their way as we assuredly carry something of them on ours. That is perhaps why to think of them is a matter not only of remembering them as they used to be but of seeing and hearing them as in some sense they are now. If they had things to say to us then, thay have things to say to us now too, nor are they always things we expect or the same things."