The communion of the saints, living and dead, is present and ongoing.
Some Protestant denominations, including Anglicans and Adventists, oppose this doctrine on the basis of "Christian mortalism" (sometimes called "soul sleep"). They point out that our Western notion of "the immortality of the soul" are predicated not on Scripture but on Platonic dualism, which treats the soul as pure and the body as corrupt, and which therefore imagines the human person as a good charioteer riding and reining in an intractable and diseased horse.
The kernel of truth in this objection must be noted: the Judeo-Christian understanding of the human person bears little resemblance to this Platonic imagery. We are embodied souls, both the "dust from the ground" and "the breath of life" (Gen. 2:7), and the resurrection promised to us is a resurrection of the body and soul. On this basis Christian mortalists argue that the soul, though alive in Christ, enters a state of sleep until woken with the bodily resurrection at the end of days, at the creation of the New Heaven and New Earth.
Though the doctrine of soul sleep has its modern adherents, it is an ancient heresy. It has existed since the earliest days of Christianity on the outskirts of Church teaching, and has never been considered orthodox. The early theologian Origen once spoke against the doctrine of soul sleep so strongly that an entire sect of Arabian dissenters was persuaded to return to the orthodox understanding (according to the church historian Eusebius).
The nearest it came to official recognition was by a pronouncement by Pope John XXII on a separate issue that might have potentially been consistent with soul sleep. Upon discussion with the College of Cardinals, the Pope corrected his statement, and his successor Pope Benedict XII recognized that corrected teaching to be ex cathedra doctrine.
Soul sleep only received a general hearing among the Protestant reformers (especially Wycliffe, Tyndale, and Luther), mostly as a utilitarian counter to the veneration of the saints. Yet even John Calvin wrote strongly against such novelties in the tract "Psychopannychia," and today, most Protestant denominations share this perspective, joining the Roman Catholic Church and the Eastern Orthodox Church in asserting the active communion of the saints.
Ultimately, the Christian doctrine of an active communion is not rooted in a Grecian notion of an immortal soul, but in the Biblical notion of an intermediate heaven preceding the New Heaven and New Earth which will become our eternal home. This is the essence of the doctrine: the saints are preserved not by some intrinsic power of our own humanity, but by the grace of God and the spirit of Christ's sonship which they share and by which by they are claimed.