As I understand the Assumption the church does NOT speak to whether or not Mary died. It is NOT anathema to believe that Mary did NOT die, but rather that she fell asleep and raised up WITHOUT dying; which is my belief. The church also ALLOWS one to believe that she DIED and then was assumed into heaven.
It was the belief of the undivided Church that the Theotokos died, lay in the grave for three days, and was assumed into heaven bodily all in imitation of her Son. Even the Latins have a church in Jerusalem at the Theotokos's tomb. They even have a statue in the style of the Byzantine Dormition icon. It was until the Immaculate Conception was defined that speculation that she did not die started in contravention of 1800 years of tradition.