I think that right now the consensus in the Catholic church has shifted solidly toward accepting the Orthodox account of her death, from what I could tell the last time I researched this matter some months ago.
The belief that she didn't die was never anything official, but I do remember seeing a Catholic priest on TV saying that the wording of the declaration intentionally avoids mentioning either her death or saying that she didn't die, since the Eastern tradition is clear that she died, but that the Western tradition is that she didn't die (in retrospect, he seems to have overstated the Western tradition.)
As I said, the Pope who declared the dogma of the Assumption is said to have held this belief. It really is just a logical conclusion of the Immaculate Conception -- no original sin, no death or corruption. It seems to have been born out of exuberant devotion to the IC.
Even today, I believe that those Catholics who believe that the Theotokos died hold that she did so voluntarily in the same way that Christ voluntarily died. Unless I misunderstand the implications of the Immaculate Conception, it would seem to me contradictory to believe the doctrine of the IC and also believe that the Theotokos would suffer inevitable physical corruption and death (as we Orthodox believe her physical corruption and death were inevitable and inexorable....)
Perhaps Annalex can clarify.
Unless it was EWTN, this variety is best avoided.
I do not think the mainstream Catholic view is that Mary did not experience death, but it might be allowable piety.
I do not think that the doctrine of Immaculate Conception has any consequence to the Orthodox mariology, as it merely shifts the point at which she achieved sinlessness to the moment of her conception, while in the East that point remains undefined, but, from what I hear, is typically thought of as happening at or before her presentation at the temple. I am not the one to ask, -- Jo has the best grasp on the Catholic doctrine this side of the Alps.