The Egyptians did not believe that mummifying a body would enable it to come back to life in the next world. They knew the physical body would remain in this world, but they preserved it, believing that the spirit of the person needed its body as a kind of base or reference point. If a body could not be recovered, had it, for example, been destroyed by fire or lost at sea, it was a serious matter. In cases such as these, a statue or a kind of reconstruction or artistic portrait would be used for the departing spirit.
An important ritual was performed at the funeral service of the departed, called The Opening of the Mouth. This ceremony was a "magical treatment" of the mouth and other apertures of the body to ensure the spirit's ability to continue to hear, see, eat, and so forth, should it need to in the spirit world. The Egyptians also performed this ceremony over statues and paintings, to endow them with a form in the afterworld.
Ruffle, John. "Ancient Egypt: Land of the Priest-King; Egyptian Temples: Houses of Power." In Eerdman's Handbook to the World's Religions. Edited by R. Pierce Beaver. Grand Rapids, Mich.: William B. Eerdman's Publishing Co., 1982.