As I’ve understood Roman Catholicism, it isn’t determined one way or the other that Mary died. A Roman Catholic is free to believe either. Catholic Answers founder Karl Keating states,
The Church has never formally defined whether she died or not, and the integrity of the doctrine of the Assumption would not be impaired if she did not die, but the almost universal consensus is that she did in fact die [Karl Keating, Catholicism and Fundamentalism (San Fransisco: Ignatius Press, 1988), p. 273].
Against this “almost universal consensus” is none other than Patrick Madrid. Of Revelation 12:1-8 he states,
This passage also shows us a vision of Mary, queen of heaven, and hints at her Assumption. The gift of suffering no corruption in the grave and of being ‘caught up’ into heaven while still alive is perfectly in accordance with Scripture [Patrick Madrid, Where is That in the Bible? (Indiana: Our Sunday Visitor, 2001), pp. 71-72].
Against this “almost universal consensus” is also the New Catholic Answer Bible:
If indeed she was free from sin, then it follows that she would not have to undergo the decay of death, which was the penalty for sin [The New Catholic Answer Bible (Kansas: Fireside Catholic Publishing, 2005) Insert F2].
On the other hand, there are Roman Catholic web pages like this stating the following:
In any case, it is at least a sententia certa (a certain teaching) that our Lady died before being raised and assumed into heaven. This is the clear and explicit tradition of the West and is maintained in a slightly less-clear (and more metaphorical) manner also in the East.
The confusion stems from the magisterial teaching of Pope Pius XII in Munificentissimus Deus. Some say he did not explicitly state that Mary died. Some Roman Catholics read this “infallible” pronouncement and state:
This certitude that Mary in fact died and was believed by the Roman Catholic Church to have died before her bodily assumption is nicely addressed by Pope Pius XII when he states in section 17 of Munificantissimu Deus… in quoting an historical source that “Adrian I, our predecessor of immortal memory, sent to the Emperor Charlemagne. These words are found in this volume: ‘Venerable to us, O Lord, is the festivity of this day on which the holy Mother of God suffered temporal death, but still could not be kept down by the bonds of death, who has begotten your Son our Lord incarnate from herself.”
Other Roman Catholics reading the same document declare:
However, the definition infallibly declared by Pius XII does not explicitly state that the Blessed Virgin suffered death: “We pronounce, declare, and define it to be a divinely revealed dogma: that the Immaculate Mother of God, the ever Virgin Mary, having completed the course of her earthly life, was assumed body and soul into heavenly glory.”
These interpretive snippets demonstrate an ironic flaw in Romanism: even their alleged infallible dogmatic pronouncements are open to interpretation. We need to continually remind Roman Catholics about this when they argue that they have some sort of superior certainty that non-Romanists do not. Roman Catholics sometimes say that if one lacks an infallible interpreter, one is left with private interpretation (as Patrick Madrid call it, “a blueprint for anarchy”). But what this often assumes is that the actual infallible pronouncements don’t need to be interpreted… but they do! One never escapes private interpretation, so when Roman Catholics raise the issue, the double standard needs to be exposed. One may respond that it really isn’t that important whether Mary died or not. That individual Roman Catholics quibble over it is no big deal. Actually though it’s simply one more example of a much bigger problem. For instance, on the fundamental issue of what are, or are not, the very Words of God, Catholics are not unified.