The non-infallible ordinary Magisterium teaches that Mary died and was resurrected from the dead, prior to her Assumption. The infallible sacred Magisterium teaches that Mary was assumed into Heaven, with body and soul united (alive).
1. infallible teachings require the full assent of faith (theological asssent, or sacred assent).
2. non-infallible teachings require only the religious submission of will and intellect (ordinary assent).
3. theological opinions vary in their weight, in their degree of certitude — but these are not magisterial teachings, and so do not require the assent of faith.
Here is my previous post on the subject of Mary’s death, resurrection, and Assumption.