It’s hard to see how her death can be disputed by Catholics considering the words of Pope Pius XII in the very document by which he dogmatically defined the Assumption.
It would, btw, be quite impossible for Eastern Catholics not to believe that the Mother of God died without doing an act of violence to their sacred Tradition. The iconography, the hymnography and the oral Tradition all teach that she did in fact die.
People like to say that the Apostolic Constitution “
Munificentissimus Deus” by which Pope Pius XII established the dogma of the Assumption in 1950 makes no mention of whether Mary died or did not die.
This is quite inaccurate. One only has to read the document to see that the Pope believes that she died. For example, he says:
"Thus, to cite an illustrious example, this is set forth in that sacramentary which 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.”
and
“As he kept you a virgin in childbirth,
thus he has kept your body incorrupt in the tomb and has glorified it by his divine act of transferring it from the tomb.”
and
“They offered more profound explanations of its meaning and nature, bringing out into sharper light the fact that this feast shows, not only that
the dead body of the Blessed Virgin Mary remained incorrupt…”
and
“she has received an eternal incorruptibility of the body together with him
who has raised her up from the tomb…”
and
“What son would not bring his mother back to life and would not bring her into paradise
after her death if he could?”
All these quotes from the papal document defining the Assumption are incontrovertible proof that the Pope taught that Mary died and was buried in a tomb and from there she was resurrected by her Son.
“MUNIFICENTISSIMUS DEUS” Pope Pius XII
http://www.ewtn.com/library/PAPALDOC/P12MUNIF.HTM